Skip to main content

Gregory Bothun

University of Oregon, Physics, Faculty Member

Followers

43

Following

15

Co-authors

15

Public Views

Goal: Re-engineering students attitudes away from entitlement and towards creative altruism.

Landmakrs:

35 years experience as a NASA contractor with various NASA science missions.

205+ published papers in peer reviewed literature. (can I stop now?)

Over 7 million dollars in overall grants from NSF and NASA;
PI on NSF RAIRE competition.

Initial Member of ISI Highly Cited Researcher in the Area of
Space Science over the period 1980-2000. (that's what you get when you publish lots of incremental knowledge papers)

Early adopter of Instructional Technology (beginning in 1993) -
produced a full suite of interactive simulations and java applets
(http://jersey.uoregon.edu); designed an implemented one of
the first wireless laptop classrooms in Higher Ed (2001)

Launched perhaps the first Science Education Outreach Website -
the Electronic Universe, on Feb 7, 1994 (http://zebu.uoregon.edu)

Phi Betta Kappa Visiting Scholar 2001-2002 (another clerical error)

Chair of first workshop on Advanced Computing and Alternative
Energy (http://www.nrel.gov/crnare) - a somewhat big deal

Developing high pixel visualization systems in combination with High Performance Parallel Computing (its my new hobby)

Specialties: Classroom design; Collaborative learning; Interdisciplinary teaching; Attitude readjustments;
asynchronous communication tools (now called flipping the classroom); development of interactive curriculum; K12 science teacher professional development; energy generation optimization; climate indexing; solving general problems in the Universe - you know - stuff that people aren't interested in.

Irrelevancies: Making the word entitlement disappear from our lexicon.

less

InterestsView All (7)

Uploads

Other Stuff by Gregory Bothun

Cosmos On a Computer

Teaching via Electrons: Networked Courseware at the University of Oregon

The University of Oregon (UO) has been recognized as a leader in campus networking and the develo... more The University of Oregon (UO) has been recognized as a leader in campus networking and the development of networked courseware. This article details the evolution of the UO campus network into an effective teaching tool and discusses both the possibilities and the limitations of interactive courseware.

Computational Research Needs in Alternative and Renewable Energy

America and the world face significant and urgent challenges rooted in the way we power and fuel ... more America and the world face significant and urgent challenges rooted in the way we power and fuel our economies. The scale of the challenge requires an unprecedented response. Global energy demand is projected to grow dramatically in the coming decades, driven by rising standards of living and by continued worldwide population increases. Developing cost-effective renewable energy sources to meet future energy demand in an environmentally responsible manner is critical to achieving both energy security and overall sustainability.

Building Educational Data Networks in Sub-Saharan Africa

Purpose: To provide a case study report of the development on data networks and initial connectiv... more

Wind Scalability and Performance in the Real World: A Performance Analysis of Recently Deployed US Wind Farms A Performance Analysis of Recently Deployed US Wind Farms

Real world performance, costs, and supply chain issues determine the rate at which wind turbines ... more Real world performance, costs, and supply chain issues determine the rate at which wind turbines can be constructed, deployed, and installed. To study this issue for the case of the USA, a sample of ~600 individual US wind farms that have come into operation as of January 2010 has been assembled and analyzed using standard statistical procedures. Results for wind farm turbine composition and overall wind energy installation rates are: (a) individual unit turbine capacity ranges from 1–5 to 3 MW, although the bulk of the installations are 2.0 MW; (b) starting in late 2012, turbines of size 2.5–3.0 MW are being installed but there are logistical transport problems that come into play on this scale; (c) as of July 1, 2014, the Horse Hollow development in Texas has the largest individual wind farm nameplate capacity of 736 MW and 10 other locations have aggregate capacity that exceed 500 MW; (d) over the period of 2006–2012, cumulative wind capacity growth was sustained at a rate of 23.7 % per annum and by January 1, 2013, total installed US wind energy was 60,000 MW; (e) if this growth rate could be sustained over a 10-year period beginning at the end of 2012, then the USA would achieve a total nameplate capacity of ~475 GW for wind, which would be approximately 40 % of the entire US electrical generating nameplate capacity; (f) due to considerable uncertainty over the future of the federal production tax credit (PTC), continued growth in 2013 did not occur and this flattening has now placed US wind energy growth on a significantly more subdued trajectory; and (g) a small extension of the PTC in 2014 allowed for an additional 4,800 MW to come on line bringing the total US installed capacity to 66,000 MW as of January 1, 2015. This is approximately 45 GW less than would have been predicted based on the previous growth rate and clearly shows the dependence of growth rate on the continuation of the PTC. Statistical analysis of real world performance and costs shows that: (a) average state measured capacity factors (CF) have a mean of 0.31 and standard deviation of 0.05; this can be compared to the average CF for European countries of 0.245 +/À 0.04. The difference in these averages is statistically significant; (b) approximately 15 % of the sample has CF > 0.4 and these sites are primarily located in Kansas, Oklahoma, and Texas; (c) recently constructed wind farms with actual published project costs indicate an average of $2 per nameplate watt; (d) CF weighted costs average about $7 per generated watt but there is considerable variation around this average; (e) CF weighted costs lower with increasing nameplate capacity which indicates an investment strategy; (f) considerations of supply chains and transport logistics indicate that the delivery of single turbine blades to the turbines that require blades of length >55 m will likely be the limiting factor that governs the rate at which new large-scale wind farms can deployed.

Distance Education: Effective Learning or Content-Free Credits

Cyberprof: The University in the Next Millennium

Educom Review, 1999

ABSTRACT

Seven Points to Overcome to Make the Virtual University Viable

The emergence of the virtual university (VU), an electronic world where students can take courses... more The emergence of the virtual university (VU), an electronic world where students can take courses without physical instruction, seems to be a foregone conclusion. Whether this new kind of university assumes the form of an Internet correspondence school or is composed of intensely interactive courseware that can effectively duplicate the mentoring process is completely unclear at this time. However, as in all true learning environments, no matter what the delivery mechanism or educational interface is, content and student engagement with the material remain key. Without that, there is no quality, and without quality no university, virtual or physical, has any purpose. Much of the motivation for the VU stems from the perceived demographic need to accommodate more students at a time when public university budgets are squeezed to the point that constructing new facilities (or even modernizing extant buildings) is simply out of the question. Many states as well as individual universities are taking both small and large steps towards real implementation of virtual classes for credit. The University of Oregon (UO), for instance, has

Developing a Digital National Library for Undergraduate Science, Mathematics, Engineering and Technology Education: Report of a Workshop

A white paper submitted to the NII 2000 Steering Committee, Technology Policy Working Group, Federal Information Infrastructure Task Force, Computer Science and Telecommunications Board, National Research Council, Washington, D.C. in response to a "Call for White Papers: Private Investment and Fe...

When technologists discuss the "Information Highway", their conversations usually revol... more When technologists discuss the "Information Highway", their conversations usually revolve around high-end technologies such as "broadband" and "Asynchronous Transfer Mode" (ATM). Unfortunately, this focus on the exclusive use of very high bandwidth solutions fails to reckon with the limitations confronting many learning institutions, and especially most of the K-12 environment, in gaining access to the "highway" or even exploring their

An electric force facilitator in descending vortex tornadogenesis

Journal of Geophysical Research Atmospheres, 2008

1] We present a novel explanation of the physical processes behind one type of cloud and ground-l... more 1] We present a novel explanation of the physical processes behind one type of cloud and ground-level tornadogenesis within a supercell. We point out that the charge separation naturally found in these large thunderstorms can potentially serve to contract the preexisting angular momentum through the additional process of the electric force. On the basis of this, we present a plausible geometry that explains why many tornado vortices begin at storm midlevel and build downward into ground-level tornadoes. A simple model based on this geometry is used to demonstrate the strength of the electric force compared to the required centripetal acceleration to maintain cloud midlevel tornado vortices measurable as tornado vortex signatures (TVSs). Furthermore, a model based on this geometry is used to get a time estimate for tornado vortex formation. From this we are able to identify a plausible value for the threshold charge density that would lead to tornadogenesis and tornado maintenance on the timescale of a few minutes. We show that the proposed geometry can explain the observations that ground-level tornadoes thrive in regions with high shear and large convective available potential energy (CAPE) and are able to make some predictions of specific measurable quantities.

99+ Cites by Gregory Bothun

THE GREAT OBSERVATORIES ALL-SKY LIRG SURVEY: COMPARISON OF ULTRAVIOLET AND FAR-INFRARED PROPERTIES

The Great Observatories All-sky LIRG Survey (GOALS) consists of a complete sample of 202 luminous... more The Great Observatories All-sky LIRG Survey (GOALS) consists of a complete sample of 202 luminous infrared galaxies (LIRGs) selected from the IRAS Revised Bright Galaxy Sample (RBGS). The galaxies span the full range of interaction stages, from isolated galaxies to interacting pairs to late stage mergers. We present a comparison of the UV and infrared properties of 135 galaxies in GOALS observed by GALEX and Spitzer. For interacting galaxies with separations greater than the resolution of GALEX and Spitzer (∼2 –6), we assess the UV and IR properties of each galaxy individually. The contribution of the FUV to the measured star formation rate (SFR) ranges from 0.2% to 17.9%, with a median of 2.8% and a mean of 4.0% ± 0.4%. The specific star formation rate (SSFR) of the GOALS sample is extremely high, with a median value (3.9 × 10 −10 yr −1) that is comparable to the highest SSFRs seen in the Spitzer Infrared Nearby Galaxies Survey sample. We examine the position of each galaxy on the IR excess–UV slope (IRX–β) diagram as a function of galaxy properties, including IR luminosity and interaction stage. The LIRGs on average have greater IR excesses than would be expected based on their UV colors if they obeyed the same relations as starbursts with L IR < 10 11 L or normal late-type galaxies. The ratio of L IR to the value one would estimate from the IRX–β relation published for lower luminosity starburst galaxies ranges from 0.2 to 68, with a median value of 2.7. A minimum of 19% of the total IR luminosity in the RBGS is produced in LIRGs and ultraluminous infrared galaxies with red UV colors (β > 0). Among resolved interacting systems, 32% contain one galaxy which dominates the IR emission while the companion dominates the UV emission. Only 21% of the resolved systems contain a single galaxy which dominates both wavelengths.

Galaxy collisions and mergers - The genesis of very powerful radio sources?

The Astrophysical Journal, 1986

A Distance Scale from the Infrared Magnitude/H I Velocity Width Relation III. The Expansion Rate Outside The Local Supercluster

Virgo dwarfs - New light on faint galaxies

The Astrophysical Journal, 1988

STAR FORMATION THRESHOLDS IN LOW SURFACE BRIGHTNESS GALAXIES

Low Surface Brightness (LSB) galaxies appear to have low star formation rates despite their often... more Low Surface Brightness (LSB) galaxies appear to have low star formation rates despite their often quite normal H I contents as judged from global H I properties such as M H /L and M HI /M r ratios. H I imaging with the Very Large Array of the National Radio Astronomy Observatory (the NRAO is operated by Associated Universities Inc. under contract with the National Science Foundation) of eight LSB galaxies shows that the H I is extended compared with the optical size and has average surface densities which are about a factor 2 lower than in High Surface Brightness (HSB) galaxies of the same type. The resolution of the H I imaging allows a rough rotation curve analysis for evaluating the critical density for star formation as formulated by Kennicutt [ApJ, 344, 685 (1989)]. The observed H I surface densities systematically fall below this critical density for most of the galaxies in this sample, in agreement with the low current star formation rates. From the optical surface photometry we conclude that the galaxies studied are in general late-type galaxies dominated by an exponential disk with a typical scale length of a few kpc. The B—R and V—I colors of the LSB galaxies are a few tenths of a magnitude bluer than those of HSB galaxies indicating that the disks of these galaxies have a mean young age.

Discovery of a huge low-surface-brightness galaxy - A protodisk galaxy at low redshift?

The Astronomical Journal, 1987

A Database for Galaxy Evolution Modeling

by Ángeles Díaz, John Beckman, cjb b, and Gregory Bothun

Publications of the Astronomical Society of the Pacific, 1996

ABSTRACT. This paper represents a collective effort to provide an extensive electronic data base ... more ABSTRACT. This paper represents a collective effort to provide an extensive electronic data base useful for the interpretation of the spectra and evolution of galaxies. A broad variety of empirical and theoretical data is discussed here, and the data are made fully available in the AAS CD-ROM Series, Vol. 7. Several empirical stellar libraries are part of this data base. They cover the ultraviolet spectral range observed with WE, optical data from different ground-based telescopes, and ground-based infrared data. Spectral type coverage depends on the wavelength, but is mostly complete for types O to M and luminosity classes V to I. A large metallicity range is covered as well. Theoretical libraries of selected spectral indices of cool stars and of stellar continuum fluxes in the temperature range 2000-50,000 Κ as well as Wolf-Rayet energy distributions are presented. Several libraries of star clusters and early-type galaxies have been selected for this data base. We discuss an extensive set of empirical spectral templates covering the wavelength region from 1200 to 9800 Â, as well as narrow-band line indices in a large number of passbands. Bench-mark spectra of nearby galaxies for model tests are included as well. We compiled numerous evolutionary models and isochrones for stars of all mass ranges of interest, wide metallicity range, and for all evolutionary phases, including the pre-main-sequence phase. The majority of the models have been computed by the Geneva and Padova groups. Evolutionary synthesis models computed by several independent groups are made available. They can be applied to old and young systems, and are optimized with respect to different aspects of input physics. The model predictions include stellar (colors, magnitudes, absorption features) and nebular (emission-line fluxes) properties. Finally, we present models of ionized gas to be used for the interpretation of active galactic nuclei and young star-forming galaxies. The community is encouraged to make use of this electronic data base and to perform a critical comparison between the individual datasets.

LOW SURFACE BRIGHTNESS GALAXIES

The properties of galaxies that are lower in surface brightness than the dark night sky are revie... more The properties of galaxies that are lower in surface brightness than the dark night sky are reviewed. There are substantial selection effects against the discovery of galaxies that are unevolved or diffuse; these systems are missing from most wide field catalogs. Low surface brightness galaxies make up a significant amount of the luminosity density of the local universe. They contribute substantial but poorly determined amounts to the census of baryons and dark matter. Low surface brightness galaxies are also relevant to the interpretation of quasar absorption lines and to the understanding of rapidly evolving galaxy populations in the more distant universe. Theories of galaxy formation and evolution must accomodate the properties of these diffuse stellar systems.

Surface photometry of low surface brightness galaxies

Low surface brightness (LSB) galaxies are galaxies dominated by an exponential disc whose central... more Low surface brightness (LSB) galaxies are galaxies dominated by an exponential disc whose central surface brightness is much fainter than the value of /tß(0) = 21.65 ± 0.30 mag arcsec-2 found by Freeman. In this paper we present broadband photometry of a sample of 21 late-type LSB galaxies. The median central surface brightness of the sample is /tß(0) = 23.2 mag arcsec " 2 and the median scale length is 3.2 kpc, showing that LSB galaxies are normal-sized galaxies. We find colours that are comparable to or bluer than those of the more widely studied 'normal' high surface brightness (HSB) galaxies. LSB galaxies are therefore not faded discs that have no current star formation. The colours cannot on the other hand be ascribed entirely to metallicity effects, but we can explain them by assuming a sporadic star formation rate scenario. LSB galaxies hence appear to be unevolved and quiescent objects, which give us an insight into the evolution of galaxies in an unperturbed environment.

Cosmos On a Computer

Teaching via Electrons: Networked Courseware at the University of Oregon

The University of Oregon (UO) has been recognized as a leader in campus networking and the develo... more The University of Oregon (UO) has been recognized as a leader in campus networking and the development of networked courseware. This article details the evolution of the UO campus network into an effective teaching tool and discusses both the possibilities and the limitations of interactive courseware.

Computational Research Needs in Alternative and Renewable Energy

America and the world face significant and urgent challenges rooted in the way we power and fuel ... more America and the world face significant and urgent challenges rooted in the way we power and fuel our economies. The scale of the challenge requires an unprecedented response. Global energy demand is projected to grow dramatically in the coming decades, driven by rising standards of living and by continued worldwide population increases. Developing cost-effective renewable energy sources to meet future energy demand in an environmentally responsible manner is critical to achieving both energy security and overall sustainability.

Building Educational Data Networks in Sub-Saharan Africa

Purpose: To provide a case study report of the development on data networks and initial connectiv... more

Wind Scalability and Performance in the Real World: A Performance Analysis of Recently Deployed US Wind Farms A Performance Analysis of Recently Deployed US Wind Farms

Real world performance, costs, and supply chain issues determine the rate at which wind turbines ... more Real world performance, costs, and supply chain issues determine the rate at which wind turbines can be constructed, deployed, and installed. To study this issue for the case of the USA, a sample of ~600 individual US wind farms that have come into operation as of January 2010 has been assembled and analyzed using standard statistical procedures. Results for wind farm turbine composition and overall wind energy installation rates are: (a) individual unit turbine capacity ranges from 1–5 to 3 MW, although the bulk of the installations are 2.0 MW; (b) starting in late 2012, turbines of size 2.5–3.0 MW are being installed but there are logistical transport problems that come into play on this scale; (c) as of July 1, 2014, the Horse Hollow development in Texas has the largest individual wind farm nameplate capacity of 736 MW and 10 other locations have aggregate capacity that exceed 500 MW; (d) over the period of 2006–2012, cumulative wind capacity growth was sustained at a rate of 23.7 % per annum and by January 1, 2013, total installed US wind energy was 60,000 MW; (e) if this growth rate could be sustained over a 10-year period beginning at the end of 2012, then the USA would achieve a total nameplate capacity of ~475 GW for wind, which would be approximately 40 % of the entire US electrical generating nameplate capacity; (f) due to considerable uncertainty over the future of the federal production tax credit (PTC), continued growth in 2013 did not occur and this flattening has now placed US wind energy growth on a significantly more subdued trajectory; and (g) a small extension of the PTC in 2014 allowed for an additional 4,800 MW to come on line bringing the total US installed capacity to 66,000 MW as of January 1, 2015. This is approximately 45 GW less than would have been predicted based on the previous growth rate and clearly shows the dependence of growth rate on the continuation of the PTC. Statistical analysis of real world performance and costs shows that: (a) average state measured capacity factors (CF) have a mean of 0.31 and standard deviation of 0.05; this can be compared to the average CF for European countries of 0.245 +/À 0.04. The difference in these averages is statistically significant; (b) approximately 15 % of the sample has CF > 0.4 and these sites are primarily located in Kansas, Oklahoma, and Texas; (c) recently constructed wind farms with actual published project costs indicate an average of $2 per nameplate watt; (d) CF weighted costs average about $7 per generated watt but there is considerable variation around this average; (e) CF weighted costs lower with increasing nameplate capacity which indicates an investment strategy; (f) considerations of supply chains and transport logistics indicate that the delivery of single turbine blades to the turbines that require blades of length >55 m will likely be the limiting factor that governs the rate at which new large-scale wind farms can deployed.

Distance Education: Effective Learning or Content-Free Credits

Cyberprof: The University in the Next Millennium

Educom Review, 1999

ABSTRACT

Seven Points to Overcome to Make the Virtual University Viable

The emergence of the virtual university (VU), an electronic world where students can take courses... more The emergence of the virtual university (VU), an electronic world where students can take courses without physical instruction, seems to be a foregone conclusion. Whether this new kind of university assumes the form of an Internet correspondence school or is composed of intensely interactive courseware that can effectively duplicate the mentoring process is completely unclear at this time. However, as in all true learning environments, no matter what the delivery mechanism or educational interface is, content and student engagement with the material remain key. Without that, there is no quality, and without quality no university, virtual or physical, has any purpose. Much of the motivation for the VU stems from the perceived demographic need to accommodate more students at a time when public university budgets are squeezed to the point that constructing new facilities (or even modernizing extant buildings) is simply out of the question. Many states as well as individual universities are taking both small and large steps towards real implementation of virtual classes for credit. The University of Oregon (UO), for instance, has

Developing a Digital National Library for Undergraduate Science, Mathematics, Engineering and Technology Education: Report of a Workshop

A white paper submitted to the NII 2000 Steering Committee, Technology Policy Working Group, Federal Information Infrastructure Task Force, Computer Science and Telecommunications Board, National Research Council, Washington, D.C. in response to a "Call for White Papers: Private Investment and Fe...

When technologists discuss the "Information Highway", their conversations usually revol... more When technologists discuss the "Information Highway", their conversations usually revolve around high-end technologies such as "broadband" and "Asynchronous Transfer Mode" (ATM). Unfortunately, this focus on the exclusive use of very high bandwidth solutions fails to reckon with the limitations confronting many learning institutions, and especially most of the K-12 environment, in gaining access to the "highway" or even exploring their

An electric force facilitator in descending vortex tornadogenesis

Journal of Geophysical Research Atmospheres, 2008

1] We present a novel explanation of the physical processes behind one type of cloud and ground-l... more 1] We present a novel explanation of the physical processes behind one type of cloud and ground-level tornadogenesis within a supercell. We point out that the charge separation naturally found in these large thunderstorms can potentially serve to contract the preexisting angular momentum through the additional process of the electric force. On the basis of this, we present a plausible geometry that explains why many tornado vortices begin at storm midlevel and build downward into ground-level tornadoes. A simple model based on this geometry is used to demonstrate the strength of the electric force compared to the required centripetal acceleration to maintain cloud midlevel tornado vortices measurable as tornado vortex signatures (TVSs). Furthermore, a model based on this geometry is used to get a time estimate for tornado vortex formation. From this we are able to identify a plausible value for the threshold charge density that would lead to tornadogenesis and tornado maintenance on the timescale of a few minutes. We show that the proposed geometry can explain the observations that ground-level tornadoes thrive in regions with high shear and large convective available potential energy (CAPE) and are able to make some predictions of specific measurable quantities.

THE GREAT OBSERVATORIES ALL-SKY LIRG SURVEY: COMPARISON OF ULTRAVIOLET AND FAR-INFRARED PROPERTIES

The Great Observatories All-sky LIRG Survey (GOALS) consists of a complete sample of 202 luminous... more The Great Observatories All-sky LIRG Survey (GOALS) consists of a complete sample of 202 luminous infrared galaxies (LIRGs) selected from the IRAS Revised Bright Galaxy Sample (RBGS). The galaxies span the full range of interaction stages, from isolated galaxies to interacting pairs to late stage mergers. We present a comparison of the UV and infrared properties of 135 galaxies in GOALS observed by GALEX and Spitzer. For interacting galaxies with separations greater than the resolution of GALEX and Spitzer (∼2 –6), we assess the UV and IR properties of each galaxy individually. The contribution of the FUV to the measured star formation rate (SFR) ranges from 0.2% to 17.9%, with a median of 2.8% and a mean of 4.0% ± 0.4%. The specific star formation rate (SSFR) of the GOALS sample is extremely high, with a median value (3.9 × 10 −10 yr −1) that is comparable to the highest SSFRs seen in the Spitzer Infrared Nearby Galaxies Survey sample. We examine the position of each galaxy on the IR excess–UV slope (IRX–β) diagram as a function of galaxy properties, including IR luminosity and interaction stage. The LIRGs on average have greater IR excesses than would be expected based on their UV colors if they obeyed the same relations as starbursts with L IR < 10 11 L or normal late-type galaxies. The ratio of L IR to the value one would estimate from the IRX–β relation published for lower luminosity starburst galaxies ranges from 0.2 to 68, with a median value of 2.7. A minimum of 19% of the total IR luminosity in the RBGS is produced in LIRGs and ultraluminous infrared galaxies with red UV colors (β > 0). Among resolved interacting systems, 32% contain one galaxy which dominates the IR emission while the companion dominates the UV emission. Only 21% of the resolved systems contain a single galaxy which dominates both wavelengths.

Galaxy collisions and mergers - The genesis of very powerful radio sources?

The Astrophysical Journal, 1986

A Distance Scale from the Infrared Magnitude/H I Velocity Width Relation III. The Expansion Rate Outside The Local Supercluster

Virgo dwarfs - New light on faint galaxies

The Astrophysical Journal, 1988

STAR FORMATION THRESHOLDS IN LOW SURFACE BRIGHTNESS GALAXIES

Low Surface Brightness (LSB) galaxies appear to have low star formation rates despite their often... more Low Surface Brightness (LSB) galaxies appear to have low star formation rates despite their often quite normal H I contents as judged from global H I properties such as M H /L and M HI /M r ratios. H I imaging with the Very Large Array of the National Radio Astronomy Observatory (the NRAO is operated by Associated Universities Inc. under contract with the National Science Foundation) of eight LSB galaxies shows that the H I is extended compared with the optical size and has average surface densities which are about a factor 2 lower than in High Surface Brightness (HSB) galaxies of the same type. The resolution of the H I imaging allows a rough rotation curve analysis for evaluating the critical density for star formation as formulated by Kennicutt [ApJ, 344, 685 (1989)]. The observed H I surface densities systematically fall below this critical density for most of the galaxies in this sample, in agreement with the low current star formation rates. From the optical surface photometry we conclude that the galaxies studied are in general late-type galaxies dominated by an exponential disk with a typical scale length of a few kpc. The B—R and V—I colors of the LSB galaxies are a few tenths of a magnitude bluer than those of HSB galaxies indicating that the disks of these galaxies have a mean young age.

Discovery of a huge low-surface-brightness galaxy - A protodisk galaxy at low redshift?

The Astronomical Journal, 1987

A Database for Galaxy Evolution Modeling

by Ángeles Díaz, John Beckman, cjb b, and Gregory Bothun

Publications of the Astronomical Society of the Pacific, 1996

ABSTRACT. This paper represents a collective effort to provide an extensive electronic data base ... more ABSTRACT. This paper represents a collective effort to provide an extensive electronic data base useful for the interpretation of the spectra and evolution of galaxies. A broad variety of empirical and theoretical data is discussed here, and the data are made fully available in the AAS CD-ROM Series, Vol. 7. Several empirical stellar libraries are part of this data base. They cover the ultraviolet spectral range observed with WE, optical data from different ground-based telescopes, and ground-based infrared data. Spectral type coverage depends on the wavelength, but is mostly complete for types O to M and luminosity classes V to I. A large metallicity range is covered as well. Theoretical libraries of selected spectral indices of cool stars and of stellar continuum fluxes in the temperature range 2000-50,000 Κ as well as Wolf-Rayet energy distributions are presented. Several libraries of star clusters and early-type galaxies have been selected for this data base. We discuss an extensive set of empirical spectral templates covering the wavelength region from 1200 to 9800 Â, as well as narrow-band line indices in a large number of passbands. Bench-mark spectra of nearby galaxies for model tests are included as well. We compiled numerous evolutionary models and isochrones for stars of all mass ranges of interest, wide metallicity range, and for all evolutionary phases, including the pre-main-sequence phase. The majority of the models have been computed by the Geneva and Padova groups. Evolutionary synthesis models computed by several independent groups are made available. They can be applied to old and young systems, and are optimized with respect to different aspects of input physics. The model predictions include stellar (colors, magnitudes, absorption features) and nebular (emission-line fluxes) properties. Finally, we present models of ionized gas to be used for the interpretation of active galactic nuclei and young star-forming galaxies. The community is encouraged to make use of this electronic data base and to perform a critical comparison between the individual datasets.

LOW SURFACE BRIGHTNESS GALAXIES

The properties of galaxies that are lower in surface brightness than the dark night sky are revie... more The properties of galaxies that are lower in surface brightness than the dark night sky are reviewed. There are substantial selection effects against the discovery of galaxies that are unevolved or diffuse; these systems are missing from most wide field catalogs. Low surface brightness galaxies make up a significant amount of the luminosity density of the local universe. They contribute substantial but poorly determined amounts to the census of baryons and dark matter. Low surface brightness galaxies are also relevant to the interpretation of quasar absorption lines and to the understanding of rapidly evolving galaxy populations in the more distant universe. Theories of galaxy formation and evolution must accomodate the properties of these diffuse stellar systems.

Surface photometry of low surface brightness galaxies

Low surface brightness (LSB) galaxies are galaxies dominated by an exponential disc whose central... more Low surface brightness (LSB) galaxies are galaxies dominated by an exponential disc whose central surface brightness is much fainter than the value of /tß(0) = 21.65 ± 0.30 mag arcsec-2 found by Freeman. In this paper we present broadband photometry of a sample of 21 late-type LSB galaxies. The median central surface brightness of the sample is /tß(0) = 23.2 mag arcsec " 2 and the median scale length is 3.2 kpc, showing that LSB galaxies are normal-sized galaxies. We find colours that are comparable to or bluer than those of the more widely studied 'normal' high surface brightness (HSB) galaxies. LSB galaxies are therefore not faded discs that have no current star formation. The colours cannot on the other hand be ascribed entirely to metallicity effects, but we can explain them by assuming a sporadic star formation rate scenario. LSB galaxies hence appear to be unevolved and quiescent objects, which give us an insight into the evolution of galaxies in an unperturbed environment.

A CATALOG OF LOW SURFACE BRIGHTNESS GALAXIES. LIST II

The second edition of a catalog of low surface brightness (LSB) galaxies is presented based on a ... more The second edition of a catalog of low surface brightness (LSB) galaxies is presented based on a visual search of the Second Palomar Sky Survey. This paper presents newly discovered LSB galaxies in 97 fields within the declination range of 0° to + 25°. The primary catalog (objects with diameters greater than 1 arcmin) contains 198 objects; the secondary catalog (30 arcsec<Z><l arcmin) contains 140 objects. H I observations are presented for 171 of these newly discovered galaxies. Our 80% detection rate yields a fairly representative velocity distribution for a sample of LSB objects. The sample is dominated by LSB disks galaxies with 2000<i><9000 km s-1. Below 2000 km s _1 a few true dwarf galaxies are found. Approximately 10% of the sample has i;> 10 000 km s" 1 and thus represents additional examples of truly large LSB galaxies. The H i redshift distribution is consistent with the hypothesis that LSB and HSB disk galaxies, in general, are drawn from the same distribution of physical size (e.g., disk scale length) modulo the curious tendency for the LSB sample to contain significantly more large-scale length galaxies which rival the prototype, Malin 1. Optical broadband and Ha imaging for a subset of the catalog is also presented confirming their quiescent nature. Our survey using the PSS-II is presently 35% complete and indicates that the UGC is 11.5% incomplete for a 1 mag arcsec-2 increase in surface brightness depth. Overall this survey demonstrates that LSB galaxies are not exclusively dwarf galaxies but encompass all Hubble types, although dominated by the late types, and all masses.

On the Nature of QSO Host Galaxies

Low-Surface-Brightness Galaxies: Hidden Galaxies Revealed

Publications of the Astronomical Society of the Pacific, 1997

... of the Pacific 109: 745-758, 1997 July Invited Review Paper Low-Surface-Brightness Galaxies: ... more

Structural characteristics and stellar composition of low surface brightness disk galaxies

The Astronomical Journal, 1994

We present UBV I surface photometry of a sample of low surface brightness (LSB) disk galaxies. LS... more We present UBV I surface photometry of a sample of low surface brightness (LSB) disk galaxies. LSB disk galaxies are fairly well described as exponential disks with no preferred value for either scale length, central surface brightness, or rotational velocity. Indeed, the distribution of scale lengths is indistinguishable from that of high surface brightness spirals, indicating that dynamically similar galaxies (e.g., those with comparable v 2 R) exist over a large range in surface density.

The Luminosity of SN 1999by in NGC 2841 and the Nature of “Peculiar” Type Ia Supernovae

The Astrophysical Journal, 2004

We present UBV RIJHK photometry and optical spectroscopy of the socalled "peculiar" Type Ia super... more We present UBV RIJHK photometry and optical spectroscopy of the socalled "peculiar" Type Ia supernova 1999by in NGC 2841. The observations began one week before visual maximum light which is well-defined by daily observations. The light curves and spectra are similar to those of the prototypical subluminous event SN 1991bg. We find that maximum light in B occurred on 1999 May 10.3 UT (JD 2,451,308.8±0.3) with B = 13.66 ± 0.02 and a color of B max − V max = 0.51 ± 0.03. The late-time color implies minimal dust extinction from the host galaxy. Our photometry, when combined with the recent Cepheid distance to NGC 2841 (Macri et al. 2001), gives a peak absolute magnitude of M B = −17.15 ± 0.23, making SN 1999by one of the least luminous Type Ia events ever observed. We estimate a decline rate parameter of ∆m 15 (B) = 1.90 mag, versus 1.93 for SN 1991bg, where 1.10 is typical for so-called "normal" events. We compare SN 1999by with other subluminous events and find that the B max − V max color correlates strongly with the decline rate and may be a more sensitive indicator of luminosity than the fading rate for these objects. We find a good correlation between luminosity and the depth of the spectral feature at 580 nm, which had been attributed solely to Si II. We show that in cooler photospheres the 580 nm feature is dominated by Ti II, which provides a simple physical explanation for the correlation. Using only subluminous Type Ia supernovae we derive a Hubble parameter of H 0 = 75 +12 −11 km s −1 Mpc −1 , consistent with values found from brighter events.

Dwarf elliptical galaxies in the Fornax cluster. II - Their structure and stellar populations

The Astronomical Journal, 1987

Modeling the Spatial Distribution of Star Formation in Interacting Disk Galaxies

The Astrophysical Journal, 1993

... 9.-NGC 4038/39 model velocity field. Dark shading is redshifted; light shading is blueshifted... more

Low Surface Brightness Galaxies in the Local Universe. I. The Catalog

by Gregory Bothun and David Sprayberry

The Astrophysical Journal Supplement Series, 1996

We present a luminosity function for low surface brightness (LSB) galaxies identified in the APM ... more We present a luminosity function for low surface brightness (LSB) galaxies identified in the APM survey of Impey et al. (1996). These galaxies have central surface brightnesses (µ(0)) in B in the range 22.0 ≤ mu(0) ≤ 25.0. Using standard maximum-likelihood estimators, we determine that the best-fit Schechter function parameters for this luminosity function (LF) are α = −1.42, M * = −18.34, and φ * = 0.0036, assuming H 0 = 100 h 100 km s −1 Mpc −1 . We compare the luminosity and number densities derived from this luminosity function to those obtained from other recent field galaxy studies and find that surveys which do not take account of the observation selection bias imposed by surface brightness are missing a substantial fraction of the galaxies in the local universe. Under our most conservative estimates, our derivation of the LF for LSB galaxies suggests that the CfA redshift survey has missed at least one third of the local galaxy population. This overlooked fraction is not enough by itself to explain the large number of faint blue galaxies observed at moderate redshift under no-evolution models, but it does help close the gap between local and moderate-redshift galaxy counts.

Extremely low surface brightness galaxies in the Fornax Cluster - Properties, stability, and luminosity fluctuations

The Astrophysical Journal, 1991

Malin 1: A Quiescent Disk Galaxy

THE GREAT OBSERVATORIES ALL-SKY LIRG SURVEY: COMPARISON OF ULTRAVIOLET AND FAR-INFRARED PROPERTIES

by Gregory Bothun and Justin Howell

The Great Observatories All-sky LIRG Survey (GOALS) consists of a complete sample of 202 luminous... more The Great Observatories All-sky LIRG Survey (GOALS) consists of a complete sample of 202 luminous infrared galaxies (LIRGs) selected from the IRAS Revised Bright Galaxy Sample (RBGS). The galaxies span the full range of interaction stages, from isolated galaxies to interacting pairs to late stage mergers. We present a comparison of the UV and infrared properties of 135 galaxies in GOALS observed by GALEX and Spitzer. For interacting galaxies with separations greater than the resolution of GALEX and Spitzer (∼2 –6), we assess the UV and IR properties of each galaxy individually. The contribution of the FUV to the measured star formation rate (SFR) ranges from 0.2% to 17.9%, with a median of 2.8% and a mean of 4.0% ± 0.4%. The specific star formation rate (SSFR) of the GOALS sample is extremely high, with a median value (3.9 × 10 −10 yr −1) that is comparable to the highest SSFRs seen in the Spitzer Infrared Nearby Galaxies Survey sample. We examine the position of each galaxy on the IR excess–UV slope (IRX–β) diagram as a function of galaxy properties, including IR luminosity and interaction stage. The LIRGs on average have greater IR excesses than would be expected based on their UV colors if they obeyed the same relations as starbursts with L IR < 10 11 L or normal late-type galaxies. The ratio of L IR to the value one would estimate from the IRX–β relation published for lower luminosity starburst galaxies ranges from 0.2 to 68, with a median value of 2.7. A minimum of 19% of the total IR luminosity in the RBGS is produced in LIRGs and ultraluminous infrared galaxies with red UV colors (β > 0). Among resolved interacting systems, 32% contain one galaxy which dominates the IR emission while the companion dominates the UV emission. Only 21% of the resolved systems contain a single galaxy which dominates both wavelengths.

Far-infrared properties of Markarian galaxies with multiple nuclei - Warm dust emission in mergers

The Astronomical Journal, 1991

LOW SURFACE BRIGHTNESS GALAXIES IN THE LOCAL UNIVERSE. III. IMPLICATIONS FOR THE FIELD GALAXY LUMINOSITY FUNCTION

We present a luminosity function for low surface brightness (LSB) galaxies identiÐed in the Autom... more We present a luminosity function for low surface brightness (LSB) galaxies identiÐed in the Automatic Plate Measuring Facility survey of Impey et al. These galaxies have central surface brightnesses [k(0)] in B in the range 22.0 ¹ k(0) ¹ 25.0. Using standard maximum likelihood estimators, we determine that the best-Ðt Schechter function parameters for this luminosity function (LF) are a \ [1.42, M* \ [18.34, and /* \ 0.0036, assuming km s~1 Mpc~1. We compare the luminosity and number den-H 0 \ 100 h 100 sities derived from this luminosity function with those obtained from other recent Ðeld galaxy studies and Ðnd that surveys that do not take account of the observational selection bias imposed by surface brightness are missing a substantial fraction of the galaxies in the local universe. Under our most conservative estimates, our derivation of the LF for LSB galaxies suggests that the CfA Redshift Survey has missed at least one-third of the local galaxy population. This overlooked fraction is not enough by itself to explain the large number of faint blue galaxies observed at moderate redshift under no-evolution models, but it does help to close the gap between local and moderate-redshift galaxy counts.

H-alpha Observations of Spiral Galaxies in Cancer, A1367 and Coma

We have used large aperture Ha photometry of 65 spiral galaxies in the Cancer, Coma, and Abell 13... more We have used large aperture Ha photometry of 65 spiral galaxies in the Cancer, Coma, and Abell 1367 clusters to compare the ionized-gas contents and star-formation rates in cluster and field spirals. Overall , we do not observe any significant deficiency of Ha emission in the cluster members. Emission strength correlates strongly with integrated galaxy colors, but only weakly with H i content. All three clusters contain several galaxies with unusually strong Ha emission, including several H i-poor objects in Coma and A1367. Thus, spirals which appear " anemic " in their morphology or exhibit weak Ha emission are not necessarily H i poor; conversely, H I poor spirals can show strong Ha emission, indicating relatively high current star-formation rates. Gas depletion time scales for some objects in the core of Coma are significantly shorter than the field, indicating rapid stellar and gaseous evolution.

A CATALOG OF RADIO, OPTICAL, AND INFRARED OBSERVATIONS OF SPIRAL GALAXIES IN CLUSTERS

We present the results of a major observational program on the luminosities, colors, and gas cont... more We present the results of a major observational program on the luminosities, colors, and gas contents of spiral galaxies in clusters of galaxies. These data have been used as part of a detailed investigation into the nature of cluster spirals and for revisions of the distance scale using the infrared Tully-Fisher relation. The observational strategies, reduction procedures, and sources of error are briefly discussed. The data include 21 cm H i observations, UBVR multiaperture photometry, and H-bznd photometry of several hundred spiral galaxies in 10 clusters.

A Wide Field CCD Survey for Low Surface Brightness Galaxies.II.Color Distributions, Stellar Populations, and Missing Baryons

The Astronomical Journal, 1997

A Wide Field CCD Survey for Low Surface Brightness Galaxies: I. Data Acquisition, Description and Initial Results

A low surface brightness (LSB) galaxy survey of the Cancer and Pegasus galaxy clusters and the lo... more A low surface brightness (LSB) galaxy survey of the Cancer and Pegasus galaxy clusters and the low density regime defined by the Great Wall, was undertaken between 1993 October 14 and 1996 April 17 using the University of Texas MacDonald Observatory 0.8 m telescope and a Loran-Fairchild 2048X2048 CCD camera. 127 galaxies were found with /¿ 5 (0)^22.0 mag/arcsec 2 , 119 of which are previously unidentified. Structural parameters [/¿ 5 (0), a, r 2 s, etc.] and colors (Johnson/Cousins U, B,V, I, & R, when possible) were determined for the galaxies. The majority of these galaxies (80%) were well fit by an exponential profile, while the remaining were either fit by a king profile (17%) or were too clumpy to be fit by any curve (3%). None of the galaxies were fit by a de Vaucouleurs (1959) r 1/4-type profile. The average central surface brightness of the sample is 23.06±0.20 mag/arcsec 2. The central surface brightness distribution of the galaxies is flat from 22.0/jl b (0) to 24.0/li b (0), at which point a sharp dropoff is observed. By eliminating the possibility the dropoff is due to selection or distance effects, we show that it is highly likely the dropoff is due to the inability for extremely LSB galaxies to form in the cluster environment. Finally, previous data have shown that LSBs are deficient in molecular gas and dust. If we assume that LSBs have no dust and correct the sample to face-on surface brightness, the lowest surface brightness disk we detected has />t 5 (0) = 27.1. However, this sample shows the same noncorrelation between inchnation and central surface brightness that is seen for the case of high surface brightness galaxies. This noncorrelation has been used as an argument to support the notion that disk galaxies are optically thick. Since its extremely unlikely that LSBs are optically thick (i.e., none are IRAS sources) this noncorrelation most likely reflects the large intrinsic range of disk galaxy surface brightness instead of variations in disk galaxy opacity.

A redshift survey of low-surface-brightness galaxies. I - The basic data

The Astronomical Journal, 1985

Discovery of a second giant low surface brightness galaxy - Further confirmation of slowly evolving disk galaxies

The Astrophysical Journal, 1990

The methodology and reliability of determining bulge-to-disk ratios for spiral galaxies

The Astronomical Journal, 1987

The Velocity Field of Clusters of Galaxies Within 100 Mpc. II. Northern Clusters

An investigation of dwarf galaxies in the Virgo cluster

The Astronomical Journal, 1985

Red, Gas-Rich Low Surface Brightness Galaxies and Enigmatic Deviations from the Tully-Fisher Relation

The Astronomical Journal, 2000

Using the refurbished 305m Arecibo Gregorian Telescope, we detected 43 low surface brightness (LS... more Using the refurbished 305m Arecibo Gregorian Telescope, we detected 43 low surface brightness (LSB) galaxies from the catalog of O'Neil, . The detected galaxies range from 22.0 mag arcsec −2 ≤ µ B (0) ≤ 25.0 mag arcsec −2 , with colors ranging from the blue through the first detection of a very red LSB galaxies (B−V = −0.7 to 1.7). The M HI /L B of these galaxies ranges from 0.1 M ⊙ /L ⊙ -50 M ⊙ /L ⊙ , showing this sample to range from very gas poor to possibly the most gas rich galaxies ever detected.

Far‐Ultraviolet and Hα Imaging of Nearby Spiral Galaxies: The OB Stellar Population in the Diffuse Ionized Gas

Astrophys J, 2001

We have compared Hα and far ultraviolet (FUV) images of 10 nearby spirals, with the goal of under... more We have compared Hα and far ultraviolet (FUV) images of 10 nearby spirals, with the goal of understanding the contribution of field OB stars to the ionization of the diffuse ionized gas (DIG) in spiral galaxies. The FUV images were obtained by the Ultraviolet Imaging Telescope (UIT) and the Hα images were obtained using various ground-based telescopes. In all of the galaxies, the F Hα /F U IT flux ratio is lower in the DIG than in the H II regions. This is likely an indication that the mean spectral type for OB stars in the field is later than that in H II regions. Comparison of the N Lyc /L U IT ratio with models of evolving stellar populations shows that the stellar population in the DIG is consistent with either an older single burst population or a steady state model with constant star formation and an initial mass function (IMF) slope steeper than α=2.35. The steady state model is probably a more realistic representation of the stellar population outside of H II regions. The steep IMF slope simulates the steep present-day mass function slope expected for field OB stars, and does not necessarily indicate that IMF slope is actually steeper than α=2.35. We compared the F Hα /F U IT ratio in the DIG of these galaxies with that in M33, in which the field OB stellar population has previously been investigated using Hubble Space Telescope images. If the mean spectral types of stars in H II regions and in the DIG are the same as in M33, and the difference in extinction between DIG and H II regions is constant among galaxies, then the analysis suggests that field stars are important sources of ionization in most galaxies, and may be the dominant source in some galaxies.

THE DISCOVERY OF CEPHEIDS AND A NEW DISTANCE TO NGC 2841 USING THE HUBBL E SPACE T EL ESCOPE1

We report on the discovery of Cepheids in the spiral galaxy NGC 2841, based on observations made ... more We report on the discovery of Cepheids in the spiral galaxy NGC 2841, based on observations made with the Wide Field Planetary Camera 2 on board the Hubble Space T elescope. NGC 2841 was observed over 12 epochs using the F555W Ðlter and over Ðve epochs using the F814W Ðlter. Photometry was performed using the DAOPHOT/ALLFRAME package. We discovered a total of 29 variables, including 18 high-quality Cepheids with periods ranging from 15 to 40 days. Period-luminosity relations in the V and I bands, based on the high-quality Cepheids, yield a reddening-corrected distance modulus of 30.74 ^ 0.23 mag, which corresponds to a distance of 14.1 ^ 1.5 Mpc. Our distance is based on an assumed LMC distance modulus of mag (D \ 50 ^ 2.5 kpc) and a metallicity depen-k 0 \ 18.50 ^ 0.10 dence of the Cepheid P-L relation of mag dex~1. c VI \ [0.2 ^ 0.2 Subject headings : Cepheids È distance scale È galaxies : individual (NGC 2841) On-line material : color Ðgures

Measuring galaxy distances from optical rotation curves

The Astronomical Journal, 1993

Sources of error in the Tully-Fisher relation - Reducing the scatter with CCD I-band surface photometry of spiral galaxies

The Astrophysical Journal, 1987

Hα Velocity Mapping of Ultraluminous Infrared Galaxies

The Astrophysical Journal, 1998

We use imaging Fabry-Pe rot observations to explore the dynamical conditions in four southern ult... more We use imaging Fabry-Pe rot observations to explore the dynamical conditions in four southern ultraluminous infrared galaxies. These galaxies all show morphological and kinematic fea-(L IR Z 1012 L _ ) tures indicative of a major merger, but they span a wide range of inferred dynamical ages : the youngest system is just past the Ðrst encounter, while the oldest has already merged into a single object. This diversity in dynamical states indicates that ultraluminous activity is not conÐned solely to late-stage mergers. The Ha emission is more spatially concentrated in the later stage mergers, in agreement with models that show that mergers drive gas inward toward the nucleus, but high luminosities are achieved even in young interactions where the Ha is quite extended. Our data indicate that physical details other than the dynamical phaseÈsuch as the internal structure or gas content of the galaxiesÈcan play a strong role in determining the luminosity evolution of merging galaxies. We also Ðnd evidence for massive star-forming complexes at large radius in the tidal debris, which reaffirms the notion that some dwarf galaxies may be spawned during the merger of more massive disk galaxies.

A POSSIBLE RELATIONSHIP BETWEEN METAL ABUNDANCE AND LUMINOSITY FOR DISK GALAXIES

Near-infrared colors have been measured for a sample of 31 late-type galaxies in the Pegasus I an... more Near-infrared colors have been measured for a sample of 31 late-type galaxies in the Pegasus I and Pisces clusters; system luminosities in the sample cover the range — 19 < M H < — 23.5. The color index (J — K) correlates strongly with the absoluteHmagnitude; lower-luminosity systems have bluer colors. These observations are consistent with the assumption that the mean metal abundance of the old disk population decreases systematically with luminosity. The systematic variation oî(B — H) with absolute H magnitude reported recently by Tully et al derives in part from this proposed systematic change of metallicity with luminosity. However, one must still posit a relative increase in the number of newly formed stars and/or a systematic smaller age for lower-luminosity disks in order to fully explain the observed (B — H), H relation.

Kinematics of star clusters in M33

The Astronomical Journal, 1991

A spatial, kinematical, and dynamical analysis of Abell 400

The Astrophysical Journal, 1992

The paper presents a detailed spatial, kinematical, and dynamical analysis for the cluster A400, ... more The paper presents a detailed spatial, kinematical, and dynamical analysis for the cluster A400, based on a nearly complete redshift survey of bright galaxies within 1 Mpc of the cluster center. A dispersed component with a high fraction of spiral galaxies at a velocity of 8200 km/s, and a background group with a mean velocity of 13,400 km/s are identified.

Musings Concerning the Possible Significance of Surface Brightness Variations in Disk Galaxies

15. Low Surface Brightness Galaxies Beyond z =0.5: Existence, Detection, and Properties

Low Surface Brightness Galaxies: Evolution without Mass Transfer

HST WFPC-2 Imaging of UGC 12695: A Remarkably Unevolved Galaxy at Low Redshift

Eprint Arxiv Astro Ph 9805161, May 12, 1998

Utilizing the F814W and F300W filters, short exposure HST WFPC-2 images were taken of UGC 12695 a... more Utilizing the F814W and F300W filters, short exposure HST WFPC-2 images were taken of UGC 12695 a nearby (z ~ 0.021) low surface brightness disk galaxy. UGC 12695 has an unusual morphology, consisting of a Y-shaped nucleus surrounded by a faint spiral arm with a number of bright H II regions interspersed throughout the galaxy. Surface photometry indicates the majority of recent star formation in this galaxy occurred in these very localized regions, most of which have a radius of < 2''. This uneven stellar distribution combined with the galaxy's overall extremely blue color and low metallicity indicates UGC 12695 is an unevolved galaxy. Some of the structural peculiarities of this galaxy arise because a number of background galaxies, previously thought to be morphological components of this galaxy, are showing through both the outer nucleus and spiral arms of UGC 12695. Surface photometry of these galaxies shows them to be fairly small (alpha < 1.8'') disk galaxies with total magnitudes ranging from 19.6 through 24.2, and central surface brightnesses between 20.2 mag/arcsec^2 < mu(0) < 23.1 mag/arcsec^2. When possible, the U, B, V, and I colors of these galaxies were measured using ground-based images, which show the galaxies to be fairly red indicatingthey are likely at redshifts z > 0.5.Inclusion of them in the photometry of UGC 12695 makes the galaxyappear significantly redder. When these galaxies are masked out, the resultant U-I color of UGC 12695 is -0.2 +/- 0.1, making it perhaps the bluest galaxy every measured in this color system and confirming its nature as a very unevolved galaxy at low redshift.Spectroscopy of these background galaxies, through the transparent disk of UGC 12695, may help to clarify its chemical evolution and current heavy element content.

LSB Galaxies and the Tully-Fisher Relation

We present Very Large Array (VLA) Hi imaging of four low surface brightness (LSB) galaxies ([OBC9... more We present Very Large Array (VLA) Hi imaging of four low surface brightness (LSB) galaxies ([OBC97] P01-3, [OBC97] C06-1, [OBC97] C04-1, [OBC97] C04-2) 1 which were thought to strongly deviate from the Tully-Fisher (TF) relation based on Arecibo singledish observations. We do not detect three of the four targeted LSB galaxies in Hi down to a 4σ limit of 0.08Jy km s −1 . We find that two of the four of these LSBs have bright galaxies at projected distances of 2.6 and 2.9 arcminutes, which have contaminated the Arecibo signal. A further examination of the Arecibo sample shows that five out of the six galaxies that were found to deviate from TF have nearby bright galaxies (within 3.5 arcmin and within the observed Hi velocity range), and we conclude that possibly 1 The official (IAU) name of these objects are originated from . For convenience, however,

Optical Detection of the H I Cloud in the Local Supercluster

Discovery of a Third Giant Low Surface Brightness Disk Galaxy

The Astrophysical Journal, 1993

H I synthesis observations of two low surface brightness dwarf galaxies in Virgo

Astronomy and Astrophysics, Aug 30, 1986

Interferometric H I observations and optical surface photometry of two dwarf irregular galaxies i... more Interferometric H I observations and optical surface photometry of two dwarf irregular galaxies in the Virgo cluster are presented. Measurements of the surface density support the postulate of a requisite H I surface density for massive star formation. Relatively large fractional gas masses and normal H I to optical diameter ratios indicate that neither galaxy shows any evidence of the effects of a cluster environment. The mass-to-light ratio for one of these galaxies is larger than expected for the relationship of M/L with morphological type derived by Faber and Gallagher, but not unusual when compared with other studies of dwarf galaxies.

Musings Concerning the Possible Significance of Surface Brightness Variations in Disk Galaxies

Nearly Normal Galaxies, 1987

The implications of the surface-brightness (SB) distribution of observed disk galaxies are explor... more The implications of the surface-brightness (SB) distribution of observed disk galaxies are explored, reviewing the results of recent investigations. Topics addressed include the SBs of catalog galaxies, proper measurements of SB, searches for new low-SB objects, and the importance of low-SB galaxies rich in H I for theoretical models of star formation. Key theoretical questions are listed, and tentative answers

Surface brightness and bandpass bias in the Hubble morphological sequence

A new HI catalog of Low Surface Brightness galaxies out to z = 0.1

Astronomy and Astrophysics, 2004

Using both the Arecibo 305m and the Nançay decimetric 100-m class radio telescopes, we have obser... more Using both the Arecibo 305m and the Nançay decimetric 100-m class radio telescopes, we have observed the H i line of 116 Low Surface Brightness (LSB) galaxies from the Bothun et al. 1985 subset of LSB galaxies in the Uppsala General Catalog. The observations had a detection rate of 70%, resulting in the new determination of H i properties for 81 galaxies. Surprisingly, roughly half of the detected objects (38) have MHI ≥ 10 10 M⊙, placing them into the category of massive LSB galaxies. As previously only ∼18 of these 'Malin 1 cousins' were known, our results have more than tripled the number of these fascinating and enigmatic systems known. Combining our results with previous studies done on the Bothun et al. catalog results in a well-defined catalog of H i properties of 526 LSB galaxies ranging in redshift space from 0 ≤ z ≤ 0.1. With this catalog in hand, we have been able to explore the parameter space occupied by LSB galaxies more completely than has been previously possible. In agreement with previous studies, our results show LSB galaxies with some of the most extreme properties of disk galaxies, including MHI /LB ratios often exceeding 10 M⊙/L⊙,B.

The ghostliest galaxies

Scientific American, Feb 1, 1997

Astronomers have found more than 1000 "low-surface-brightness" galaxies, significantly altering o... more

Hidden Galaxies Revealed

Eprint Arxiv Astro Ph 9702156, Feb 18, 1997

In twenty years, low surface brightness (LSB) galaxies have evolved from being an idiosyncratic n... more In twenty years, low surface brightness (LSB) galaxies have evolved from being an idiosyncratic notion to being one of the major baryonic repositories in the Universe. The story of their discovery and the characterization of their properties is told here. Their recovery from the noise of the night sky background is a strong testament to the severity of surface brightness selection effects. LSB galaxies have a number of remarkable properties which distinguish them from the more familiar Hubble Sequence of spirals. The two most important are 1) they evolve at a significantly slower rate and may well experience star formation outside of the molecular cloud environment, 2) they are embedded in dark matter halos which are of lower density and more extended than the halos around high surface brightness (HSB) disk galaxies. Compared to HSB disks, LSB disks are strongly dark matter dominated at all radii and show a systematic increase in M/L with central surface brightness. In addition, the recognition that large numbers of LSB galaxies actually exist has changed the form of the galaxy luminosity function and has clearly increased the space density of galaxies at z = 0. Recent CCD surveys have uncovered a population of red LSB disks that may be related to the excess of faint blue galaxies detected at moderate redshifts. LSB galaxies offer us a new window into galaxy evolution and formation which is every bit as important as those processes which have produced easy to detect galaxies. Indeed, the apparent youth of some LSB galaxies suggest that galaxy formation is a greatly extended process. While the discovery of LSB galaxies have lead to new insights, it remains unwise to presume that we now have a representative sample which encompasses all galaxy types and forms.

Hunting the elusive invisible galaxy

The Thrill of Extragalactic Exploration As Told by Leading Experts, 2000

Metallicity estimates for H II regions in M81

The Astronomical Journal, 1984

The Distances and Properties of a sample of Sc I Galaxies

THE AGES OF DISTURBED FIELD ELLIPTICAL GALAXIES. I. GLOBAL PROPERTIES

Near-infrared images of elliptical galaxies with morphological signatures of recent merger activi... more Near-infrared images of elliptical galaxies with morphological signatures of recent merger activity have been obtained. If this merger activity stimulated signiÐcant and distributed star formation within the region deÐned by then JHK photometry in this region should detect the presence of an R \ 1.5R e , intermediate-age stellar population associated with this event. Our observations, however, show that these galaxies occupy the same locus of points in the J[H versus H[K plane as elliptical galaxies with no signs of recent merger activity. This strongly constrains the global fractional amount of intermediate-age (1È3 Gyr) stellar mass to be no more than 10%È15%, and in most cases the data are consistent with all the stellar mass being old (T [ 10 Gyr) and metal-rich ([Fe/H] º [0.3). We argue that any recent merger activity was, therefore, not accompanied by a signiÐcant episode of distributed star formation within the region deÐned by and that the bluer UBV colors often observed in this region for R \ 1.5R e some of these galaxies are due to the accretion of lower mass companions or relative abundance di †er-ences. The possibility of a strongly centralized starburst resulting from the merger, instead of a more distributed star-forming episode, is fully discussed in Paper II of this series, in which similar tight constraints on this activity will be discussed.

THE AGES OF DISTURBED FIELD ELLIPTICAL GALAXIES. II. CENTRAL PROPERTIES

The formation of elliptical galaxies via the merger of gas-rich disks has received considerable a... more The formation of elliptical galaxies via the merger of gas-rich disks has received considerable attention in recent years, with many studies strongly supporting the merger hypothesis. When investigated in detail, the dynamics of a major merger that produces a high phase-space density of material (e.g., the center of an elliptical galaxy) invariably produces the ubiquitous signature of a centrally concentrated burst of star formation. We have searched for this central burst of star formation in a sample of Ðeld elliptical galaxies that exhibit morphological Ðne structure thought to be indicative of merging. Out of this sample of 32 galaxies, we Ðnd only two galaxies, NGC 3610 and NGC 5322, with sufficiently red central near-IR colors to be consistent with the asymptotic giant branch light reÑective of the central burst of star formation a few gigayears ago. Using NGC 3610 and 5322 as case studies, we discuss possible astrophysical links between global and central properties and their implied constraints on elliptical galaxy formation and evolution. In particular, we conclude that the available evidence argues against mergers of disk galaxies within the last 3È4 Gyr as being the primary formation mechanism for morphologically disturbed Ðeld elliptical galaxies.

The Neutral Hydrogen Content of Red Spiral Galaxies

Very red, yet H I rich galaxies

The Astronomical Journal, 1983

Searching for the Optimal Means of Comparative H I Analysis

A Near-IR Spectroscopic Survey of the Central Regions of Field Ellipticals: Continued

We propose to obtain central region K-band spectra for a sample of N ~ 30 field elliptical galaxi... more We propose to obtain central region K-band spectra for a sample of N ~ 30 field elliptical galaxies. An analysis of the central near-IR colors of these galaxies suggests that some of these galaxies may contain first-ascent giant branches (FGB) similar to the unusual FGB seen in the metal-rich Galactic globular clusters Liller 1 and NGC 6440. We wish to test this hypothesis by measuring the equivalent widths of the Na I 2.207(micron) and Ca I 2.263(micron) as well as the CO 2.36(micron) index. These new EW and CO index measurements will be compared to previously published data for K and M giants in the Local Solar Neighborhood, Baade's Window, and the Liller 1 and NGC 6440 clusters. These spectra can also be used to assess cosmic dispersion in the elliptical galaxy stellar population properties, which has important implications for SBF distance measurements and the study of high- redshift galaxies.

Beyond the Hubble Sequence

Beyond the Hubble sequence : what physical processes shape galaxies?

Sky and Telescope, 2000

Data and Analysis of a Large Sample of Early-Type Galaxies and The Fundamental Plane of Nearby Clusters

Near-infrared imaging of ellipticals: surface brightness profiles and photometry

Monthly Notices of the Royal Astronomical Society, Apr 30, 2003

We present near-infrared K-band imaging of a large sample of candidate merger remnant galaxies an... more We present near-infrared K-band imaging of a large sample of candidate merger remnant galaxies and Hickson Compact Group ellipticals. We derive light profile indices, effective radii and surface brightnesses, as well as total K-band magnitudes. We find that the light distributions of the merger remnant candidates are consistent with those of `normal' ellipticals, and scatter around a mean profile index of (1/n) = 0.20. Many of our sample galaxies have surface brightness profiles that are not well described by a de Vaucouleurs law (1/n= 0.25), and we discuss the implications of this on the derived total magnitudes. Comparing the total K magnitudes calculated by extrapolating a de Vaucouleurs profile and those derived using a generalized Sérsic form, we find that a significant bias is introduced if the de Vaucouleurs law is not a good description of the actual light profile.

The Arecibo Galaxy Environment Survey – II. A H I view of the Abell cluster 1367 and its outskirts

We present 21 cm H I line observations of 5 × 1 deg 2 centred on the local Abell cluster 1367 obt... more We present 21 cm H I line observations of 5 × 1 deg 2 centred on the local Abell cluster 1367 obtained as part of the Arecibo Galaxy Environment Survey. One hundred sources are detected (79 new H I measurements and 50 new redshifts), more than half belonging to the cluster core and its infalling region. Combining the H I data with Sloan Digital Sky Survey (SDSS) optical imaging, we show that our H I selected sample follows scaling relations similar to the ones usually observed in optically selected samples. Interestingly, all galaxies in our sample appear to have nearly the same baryon fraction independently of their size, surface brightness and luminosity. The most striking difference between H I and optically selected samples resides in their large-scale distribution: whereas optical and X-ray observations trace the cluster core very well, in H I there is almost no evidence of the presence of the cluster. Some implications on the determination of the cluster luminosity function and H I distribution for samples selected at different wavelength are also discussed.

The evolution of disk galaxies and the S0 problem, revisited

The Astrophysical Journal Supplement Series, 1982

The Arecibo Galaxy Environment Survey – II. A H I view of the Abell cluster 1367 and its outskirts

We present 21 cm H I line observations of 5 × 1deg 2 centred on the local Abell cluster 1367 obta... more We present 21 cm H I line observations of 5 × 1deg 2 centred on the local Abell cluster 1367 obtained as part of the Arecibo Galaxy Environment Survey. One hundred sources are detected (79 new H I measurements and 50 new redshifts), more than half belonging to the cluster core and its infalling region. Combining the H I data with Sloan Digital Sky Survey (SDSS) optical imaging, we show that our H I selected sample follows scaling relations similar to the ones usually observed in optically selected samples. Interestingly, all galaxies in our sample appear to have nearly the same baryon fraction independently of their size, surface brightness and luminosity. The most striking difference between H I and optically selected samples resides in their large-scale distribution: whereas optical and X-ray observations trace the cluster core very well, in H I there is almost no evidence of the presence of the cluster. Some implications on the determination of the cluster luminosity function and H I distribution for samples selected at different wavelength are also discussed.

Are "Anemic" Spirals Deficient in Neutral Hydrogen?

The relationships between morphological type and quantitative measures in the cluster environment

Publications of the Astronomical Society of the Pacific, 1982

ABSTRACT

Spiral galaxies in clusters. I - Neutral hydrogen observations in Abell 1367, Coma, and Zwicky 74-23 /1400.4 + 0949/

The Astronomical Journal, 1981

Spiral galaxies in clusters. II - Neutral hydrogen observations in Cancer, Hercules /A 2151/, and Pegasus I

The Astronomical Journal, 1981

Spiral galaxies in clusters. III - Gas-rich galaxies in the Pegasus I cluster of galaxies. IV - The H I color properties of spirals in nine clusters

Astron J, 1982

Results of a 21-cm and optical survey of disk galaxies in the vicinity of the Pegasus I cluster o... more Results of a 21-cm and optical survey of disk galaxies in the vicinity of the Pegasus I cluster of galaxies is reported, in addition to the results of a 21-cm H I and UBV photometric survey of 235 disk galaxies in nine nearby clusters. A substantial number of blue, gas-rich galaxies are revealed for the Pegasus I cluster, and with few exceptions, the disk systems in the cluster retain large amounts of neutral hydrogen, which suggests that environmental processes have not yet removed substantial amounts of gas from these disk galaxies. The analysis of 235 disk galaxies in nearby clusters indicates that most of the clusters do not preferentially contain gas deficient spirals. The large amount of H I retained by the galaxies is not well correlated with color.

Spiral Galaxies in Clusters - Part Four - the HI Color Properties of Spirals in Nine Clusters

The Astronomical Journal, 1982

Spiral galaxies in clusters. V - Radial gradients in Coma and A1367

The Astronomical Journal, 1984

... The presence ofboth blue and red spirals in the central regions of Coma thus demonstrates a f... more ... The presence ofboth blue and red spirals in the central regions of Coma thus demonstrates a fairly wide range of spiral &amp;quot;types&amp;quot; in this region. Moreover, Kennicutt, Bothun, and Schommer (1983) find no radial gradient in the intensity of Ha emission for the spirals in Coma. ...

The Infrared Color-Magnitude and Color-Gas Content Relations for Cluster Spirals

Isophotal diameters of cluster spirals

The Astrophysical Journal Supplement Series, 1987

Multi-Wavelength Observations of Spiral Galaxies in Clusters of Galaxies

ABSTRACT

The Chemical Composition of Distant Globular Clusters: Are There any Metal-Poor Clusters?

Globular Cluster Population of Hickson Compact Group 22a and 90c

The Astrophysical Journal, 2001

We present the first measurement of the globular cluster populations of galaxies in Hickson compa... more We present the first measurement of the globular cluster populations of galaxies in Hickson compact groups, in order to investigate the effect of these high density environments on the formation and evolution of globular cluster systems. Based on V and R band images that we obtained of HCG 22a and HCG 90c with the ESO New Technology Telescope (NTT), we find a total globular cluster population of 1590 ± 854 for HCG 22a and 2136 ± 718 for 90c. The specific frequency for HCG 22a was found to be S N = 1.9 ± 1.0 and S N = 3.4 ± 1.1 for HCG 90c. A power-law fit to the globular cluster radial profile of HCG 22a yields σ ∼ R −2.01±0.30 and for HCG 90c we found σ ∼ R −1.20±0.16 . A comparison of the globular cluster radial profiles with the surface brightness of the parent galaxy shows that the globular cluster systems are at least as extended as the halo light. The measured values for the specific frequency are consistent with a scenario in which the host galaxies were in a low density "field-like" environment when they formed their globular cluster systems.

The globular-cluster system of the edge-on Sb galaxy NGC 5170

Publications of the Astronomical Society of the Pacific, 1990

Extensive profile-fitting photometry of three V-band CCD frames containing the Sb galaxy NGC 5170... more Extensive profile-fitting photometry of three V-band CCD frames containing the Sb galaxy NGC 5170 and two frames well removed from the galaxy are presented. The radial density distribution for the galaxy is in agreement with results for other galaxies. The problem of distance determination by comparison of the globular cluster luminosity functions is addressed using a Fisher-Tully measurement. The results suggest that the distance modulus is (m - M) = 32.3 + or - 0.3. From this value, the total population of the globular cluster system is found to be about 815 + or - 320.

Globular Clusters in Galaxies Beyond the Local Group VI: The Spiral Galaxy NGC 2683

Star counts around the nearby spiral galaxy NGC 2683 show it to have a globular cluster system at... more Star counts around the nearby spiral galaxy NGC 2683 show it to have a globular cluster system at least as populous as the cluster system in our galaxy. We detect 100 + 31 globular clusters, and we estimate that the total cluster population is ^321 + 108. The specific frequency relative to the total galaxy light is *5^2.2 ± 0.8, and relative to the spheroid luminosity is S (spheroid) ^9 ± 3.

0351+026 - A QSO spawned by interacting galaxies

Astron J, 1982

The results of a detailed investigation into the nature of the H I-rich quasi-stellar object 0351... more The results of a detailed investigation into the nature of the H I-rich quasi-stellar object 0351+026 are presented. An improved H I profile reveals the presence of two distinct components. A high-quality CCD image clearly shows the presence of two galaxies. The brighter galaxy hosts the QSO while the less luminous companion has a prominent, apparently stellar nucleus. Moreover, this image also shows streamers of nebulosity emanating from the two galaxies and has an overall morphology which is highly reminiscent of that seen in other strongly interacting galaxies. Optical spectroscopy of the system shows that the forbidden O III emission lies between the two nuclei and there is strong evidence of stellar absorption lines in both the host and companion galaxies. Overall, the data suggest that this system represents a violent encounter between two low-luminosity H I-rich galaxies. The possibility exists that this collision has triggered the QSO activity in the brighter galaxy.

TRACING POLYCYCLIC AROMATIC HYDROCARBONS AND WARM DUST EMISSION IN THE SEYFERT GALAXY NGC 1068

We present a study of the nearby Seyfert galaxy NGC 1068 using mid-and far-infrared data acquired... more We present a study of the nearby Seyfert galaxy NGC 1068 using mid-and far-infrared data acquired with the IRAC, IRS, and MIPS instruments aboard the Spitzer Space Telescope. The images show extensive 8 and 24 m emission coinciding with star formation in the inner spiral approximately 15 00 (1 kpc) from the nucleus and a bright complex of star formation $47 00 (3 kpc) southwest of the nucleus. The brightest 8 m polycyclic aromatic hydrocarbon (PAH) emission regions coincide remarkably well with knots observed in an H image. Strong PAH features at 6.2, 7.7, 8.6, and 11:3 m are detected in IRS spectra measured at numerous locations inside, within, and outside the inner spiral. The IRAC colors and IRS spectra of these regions rule out dust heated by the active galactic nucleus (AGN) as the primary emission source; the spectral energy distributions are dominated by starlight and PAH emission. The equivalent widths and flux ratios of the PAH features in the inner spiral are generally consistent with conditions in a typical spiral galaxy interstellar medium (ISM). Interior to the inner spiral, the influence of the AGN on the ISM is evident via PAH flux ratios indicative of a higher ionization parameter and a significantly smaller mean equivalent width than observed in the inner spiral. The brightest 8 and 24 m emission peaks in the disk of the galaxy, even at distances beyond the inner spiral, are located within the ionization cones traced by [O iii]/H, and they are also remarkably well aligned with the axis of the radio jets. Although it is possible that radiation from the AGN may directly enhance PAH excitation or trigger the formation of OB stars that subsequently excite PAH emission at these locations in the inner spiral, the orientation of collimated radiation from the AGN and star formation knots in the inner spiral could be coincidental. The brightest PAH-and 24 mYemitting regions are also located precisely where two spiral arms of molecular gas emerge from the ends of the inner stellar bar; this is consistent with kinematic models that predict maxima in the accumulation and compression of the ISM, where gas gets trapped within the inner Lindblad resonance of a large stellar bar that contains a smaller, weaker bar.

THE BURIED STARBURST IN THE INTERACTING GALAXY II Zw 096 AS REVEALED BY THE SPITZER SPACE TELESCOPE

by Gregory Bothun, Vassilis Charmandaris, Kevin Xu, and Joseph Mazzarella

An analysis of data from the Spitzer Space Telescope, Hubble Space Telescope, Chandra X-ray Obser... more An analysis of data from the Spitzer Space Telescope, Hubble Space Telescope, Chandra X-ray Observatory, and AKARI Infrared Astronomy Satellite is presented for the z = 0.036 merging galaxy system II Zw 096 (CGCG 448-020). Because II Zw 096 has an infrared luminosity of log(L IR /L) = 11.94, it is classified as a Luminous Infrared Galaxy (LIRG), and was observed as part of the Great Observatories All-sky LIRG Survey (GOALS). The Spitzer data suggest that 80% of the total infrared luminosity comes from an extremely compact, red source not associated with the nuclei of the merging galaxies. The Spitzer mid-infrared spectra indicate no high-ionization lines from a buried active galactic nucleus in this source. The strong detection of the 3.3 μm and 6.2 μm polycyclic aromatic hydrocarbon emission features in the AKARI and Spitzer spectra also implies that the energy source of II Zw 096 is a starburst. Based on Spitzer infrared imaging and AKARI near-infrared spectroscopy, the star formation rate is estimated to be 120 M yr −1 and >45 M yr −1 , respectively. Finally, the high-resolution B-, I-, and H-band images show many star clusters in the interacting system. The colors of these clusters suggest at least two populations—one with an age of 1–5 Myr and one with an age of 20–500 Myr, reddened by 0–2 mag of visual extinction. The masses of these clusters span a range between 10 6 and 10 8 M. This starburst source is reminiscent of the extranuclear starburst seen in NGC 4038/9 (the Antennae Galaxies) and Arp 299 but approximately an order of magnitude more luminous than the Antennae. The source is remarkable in that the off-nuclear infrared luminosity dominates the entire system.

A numerical study of star formation in interacting disk galaxies

The Astrophysical Journal, 1991

Observations of peculiar galaxies in clusters of galaxies

The Astronomical Journal, 1982

The Wasilewski sample of emission-line galaxies - Follow-up CCD imaging and spectroscopic and IRAS observations

Astrophysical Journal Supplement Series, 1989

The results of an extensive imaging and spectroscopic follow-up of the objective prism-selected e... more The results of an extensive imaging and spectroscopic follow-up of the objective prism-selected emission line galaxy (ELG) sample of Wasilewski (1982) are presented. Fluxes at 12, 25, 60, and 100 microns were also obtained from the coadded IRAS survey data. ELGs found by objective prism surveys are found to be generally small and underluminous galaxies which usually have higher than

NGC 2442: Tidal Encounters and the Evolution of Spiral Galaxies

The Astrophysical Journal, 1997

Using imaging Fabry-Perot data, we study the star-forming properties and kinematics of the nearby... more Using imaging Fabry-Perot data, we study the star-forming properties and kinematics of the nearby barred spiral galaxy NGC 2442. The Ha emission is very localized along the strong spiral arms of the galaxy, and shows a marked asymmetry between the sharp, well-deÐned northern tidal arm and the weaker southern arm. The Ha velocity Ðeld appears highly distorted, with a rapidly rotating nuclear component. We Ðnd evidence for strong noncircular motions along the northern arm, coincident with the pronounced dust lane and regions of intense star formation. The strong asymmetries, the disturbed velocity Ðeld, and the presence of a perturbed companion suggest that we are witnessing a strong kinematic response to a close interaction, which has redistributed the star formation activity throughout the disk of NGC 2442. Dynamical modeling of the NGC 2442 system supports this hypothesis and suggests that the regions of strongest star formation are coincident with strong shocks occurring along the tidally perturbed northern arm. Despite this strong redistribution of the gas on small scales, this galaxy does not show a signiÐcant departure from the Tully-Fisher relation, nor does it appear to be experiencing any strong starburst. Moreover, our models predict that in a few times 108 yr, NGC 2442 will have recovered from this Ðrst tidal encounter and will experience another passageÈand ultimately a mergerÈ in a few gigayears. This merger may provoke stronger, permanent changes in the structural properties of the galaxy, depending on the detailed response of the disk. Given the environment of many disk galaxies, this tidal encounter cycle seems likely to be a normal phase of disk galaxy evolution.

The peculiar disk galaxy UGC 7576

The Astrophysical Journal, 1982

Was 49: An Interacting Pair of Seyfert Galaxies *

The peculiar galaxy IC 1182

Astrophys J, 1981

Recent 21-cm observations of the peculiar elliptical galaxy IC 1182 in the Hercules cluster of ga... more Recent 21-cm observations of the peculiar elliptical galaxy IC 1182 in the Hercules cluster of galaxies reveal the presence of a large quantity of neutral hydrogen. The distance-independent ratio of hydrogen mass to optical luminosity that is derived, approximately equal to 0.7 times the solar ratio, is in fact more appropriate for a fairly late-type (Sc or Scd) spiral. The integrated colors, however, are appropriate for an earlier type galaxy in agreement with the morphological classification. Spectrophotometry of the jet associated with the galaxy resemble normal H II region spectra, which seems inconsistent with a model of violent ejection from the galaxy nucleus. Together with Arp's (1972) plate of the galaxy showing low surface-brightness shreds of nebulosity around IC 1182, these data seem consistent with a collision model involving a gas-rich spiral and an elliptical. Such a collision may have given rise to the observed nuclear emission lines as well.

INVESTIGATION OF DUAL ACTIVE NUCLEI, OUTFLOWS, SHOCK-HEATED GAS, AND YOUNG STAR CLUSTERS IN MARKARIAN 266

by Gregory Bothun, D. Kimes, and C. Ishida

Results of observations with the Spitzer, Hubble, GALEX, Chandra, and XMM-Newton space telescopes... more Results of observations with the Spitzer, Hubble, GALEX, Chandra, and XMM-Newton space telescopes are presented for the luminous infrared galaxy (LIRG) merger Markarian 266. The SW (Seyfert 2) and NE (LINER) nuclei reside in galaxies with Hubble types SBb (pec) and S0/a (pec), respectively. Both companions are more luminous than L * galaxies and they are inferred to each contain a ≈ 2.5 × 10 8 M black hole. Although the nuclei have an observed hard X-ray flux ratio of f X (NE)/f X (SW) = 6.4, Mrk 266 SW is likely the primary source of a bright Fe Kα line detected from the system, consistent with the reflection-dominated X-ray spectrum of a heavily obscured active galactic nucleus (AGN). Optical knots embedded in an arc with aligned radio continuum radiation, combined with luminous H 2 line emission, provide evidence for a radiative bow shock in an AGN-driven outflow surrounding the NE nucleus. A soft X-ray emission feature modeled as shock-heated plasma with T ∼ 10 7 K is cospatial with radio continuum emission between the galaxies. Mid-infrared diagnostics provide mixed results, but overall suggest a composite system with roughly equal contributions of AGN and starburst radiation powering the bolometric luminosity. Approximately 120 star clusters have been detected, with most having estimated ages less than 50 Myr. Detection of 24 μm emission aligned with soft X-rays, radio continuum, and ionized gas emission extending ∼34 (20 kpc) north of the galaxies is interpreted as ∼2 × 10 7 M of dust entrained in an outflowing superwind. At optical wavelengths this Northern Loop region is resolved into a fragmented morphology indicative of Rayleigh–Taylor instabilities in an expanding shell of ionized gas. Mrk 266 demonstrates that the dust " blow-out " phase can begin in a LIRG well before the galaxies fully coalesce during a subsequent ultraluminous infrared galaxy (ULIRG) phase, and rapid gas consumption in luminous dual AGNs with kiloparsec-scale separations early in the merger process may explain the paucity of detected binary QSOs (with parsec-scale orbital separations) in spectroscopic surveys. An evolutionary sequence is proposed representing a progression from dual to binary AGNs, accompanied by an increase in observed L x /L ir ratios by over two orders of magnitude.

1E 1415.6 +2257: An X-ray Selected BL Lac Object in a Luminous Galaxy

The Effect of Local Galaxy Density on the Radio Emitting Properties of Galaxies

CCD imaging and neutral hydrogen emission in IZw1 and other low-redshift QSOs/AGNs

The Astronomical Journal, 1984

Was 49 - Mirror for a hidden Seyfert 1 nucleus

The Astronomical Journal, 1992

... VOLUME 104, NUMBER 3 SEPTEMBER 1992 WAS 49: MIRROR FOR A HIDDEN SEYFERT 1 NUCLEUS EDWARD C. M... more

Detection of Extended Nebulosity and Neutral Hydrogen Emission in the Low Redshift QSO 0351 + 026

0351+026 - A QSO spawned by interacting galaxies

The Astronomical Journal, 1982

Quasars as the Active Nuclei of Interacting Galaxies: A Spectroscopic Investigation *

A search for dead quasars among nearby luminous galaxies. I - The stellar kinematics in the nuclei of NGC 2613, NGC 4699, NGC 5746, and NGC 7331

Astrophys J, 1993

Observations and analysis are presented of four spiral galaxies with M(B) = -20 or less: NGC 2613... more Observations and analysis are presented of four spiral galaxies with M(B) = -20 or less: NGC 2613, NGC 4699, NGC 5746, and NGC 7331. Optical long-slit spectra of the galaxies are used to obtain the stellar kinematics as a function of radius, and the surface brightness profiles are obtained from broadband images or the calibrated intensity profile along the spectrograph slit. Dynamical models of each galaxy are constructed using a constrained maximum entropy technique to investigate if the observed stellar kinematics require the presence of a central unseen mass. For all four galaxies it is found that the models without central black holes and with constant M/L as a function of radius fit the observational data. None of these galaxies shows compelling evidence of harboring a black hole of about a billion solar masses. Dynamical models that include a central black hole with this mass fit the observations of NGC 2613, NGC 4699, and NGC 5746, but not NGC 7331.

A Search for Dead QSOs Among Nearby Luminous Galaxies *

Bulletin of the American Astronomical Society, Sep 1, 1990

The use of dwarf elliptical galaxies as distance indicators - The relative distances between Virgo, Fornax, and Centaurus

The Astronomical Journal, 1989

Neutral Hydrogen Observations of Four Dwarf Irregular Galaxies in the Virgo Cluster

Infrared Photometry and Optical Spectroscopy of Dwarf Galaxies in the Virgo Cluster

An optical counterpart to the H I cloud in the local supercluster

The Astrophysical Journal, 1990

ABSTRACT

Un ph�nom�ne Seyfert dans une galaxies naine isol�e

Ann Phys Paris, 1987

The discovery of a Seyfert 2 activity in a dwarf galaxy is reported. Spectra obtained in the opti... more The discovery of a Seyfert 2 activity in a dwarf galaxy is reported. Spectra obtained in the optical show that the emission-lines are resolved and have a narrow and a broad component blue shifted. CCD images reveal an underlying extended component with an exponential disk luminosity profile. This discovery shows that any galaxy type can sustain nuclear activity and raises interesting questions on how the process is fueled.

The Discovery of a SEYFERT2 Activity in a Dwarf Galaxy

Medium-resolution spectroscopy of nucleated dwarf elliptical galaxies

The Astrophysical Journal, 1988

A dwarf galaxy with Seyfert characteristics

The Astronomical Journal, 1987

Companions to Isolated Elliptical Galaxies: Revisiting the Bothun‐Sullivan Sample

The Astrophysical Journal, 2004

We investigate the number of physical companion galaxies for a sample of relatively isolated elli... more We investigate the number of physical companion galaxies for a sample of relatively isolated elliptical galaxies. The NASA/IPAC Extragalactic Database (NED) has been used to reinvestigate the incidence of satellite galaxies for a sample of 34 elliptical galaxies, first investigated by using a visual inspection of Palomar Sky Survey prints out to a projected search radius of 75 kpc. We have repeated their original investigation using data cataloged data in NED. Nine of these ellipticals appear to be members of galaxy clusters: the remaining sample of 25 galaxies reveals an average of +1.0 ± 0.5 apparent companions per galaxy within a projected search radius of 75 kpc, in excess of two equal-area comparison regions displaced by 150-300 kpc. This is significantly larger than the +0.12 ± 0.42 companions/galaxy found by Bothun & Sullivan for the identical sample. Making use of published radial velocities, mostly available since the completion of the Bothun-Sullivan study, identifies the -2physical companions and gives a somewhat lower estimate of +0.4 companions per elliptical. This is still a factor of 3× larger than the original statistical study, but given the incomplete and heterogeneous nature of the survey redshifts in NED, it still yields a firm lower limit on the number (and identity) of physical companions. An expansion of the search radius out to 300 kpc, again restricted to sampling only those objects with known redshifts in NED, gives another lower limit of 4.5physical companions per galaxy. (Excluding five elliptical galaxies in the Fornax cluster this average drops to 3.5 companions per elliptical.) These physical companions are individually identified and listed, and the ensembleaveraged radial density distribution of these associated galaxies is presented. For the ensemble, the radial density distribution is found to have a fall-off consistent with ρ ∝ R −0.5 out to approximately 150 kpc. For non-Fornax cluster companions the fall-off continues out to the 300-kpc limit of the survey. The velocity dispersion of these companions is found to reach a maximum of 350 km/sec at around 120 kpc, after which they fall at a rate consistent with Keplerian. This fall-off may then indicate the detection of a cut-off in the mass-density distribution in the elliptical galaxies' dark-matter halo at ∼100 kpc.

Exploratory IR Photometry and Optical Spectroscopy of Dwarf Galaxies in the Virgo Cluster

An upper limit on the H I content of the Carina dwarf spheroidal galaxy

The Astrophysical Journal, 1990

An HI Survey of Actively Star-Forming Dwarf Galaxies

Bulletin of the American Astronomical Society, May 1, 1993

We present the results of a survey of the HI content of a large, complete sample of actively star... more We present the results of a survey of the HI content of a large, complete sample of actively star-forming dwarf galaxies. All observations were obtained with the 305-m telescope of the Arecibo Observatory. The sample consists of all galaxies cataloged in the Markarian, Case, Michigan, Wasilewski, and Haro surveys which were known to have M_B > -17.0 and which lie within the Arecibo declination range. In all, 139 galaxies were observed, of which 122 were detected. The data consist of high S/N HI profiles, obtained with high velocity resolution (1 -- 2 km/s channel spacing) to ensure adequate sampling of the profiles, which are often quite narrow. The neutral gas properties of the sample are analyzed and combined with optical data when the latter are available. These objects possess a surprisingly wide range in the levels of their neutral gas content. Some of these star-forming galaxies appear to be very gas-poor even when compared with samples of less active dwarfs, but many others have large HI mass to blue light ratios. It is suggested that many of the currently starbursting dwarfs evolved from progenitor galaxies which initially had extremely high MHI/L_B and were likely to be ultra-low surface brightness galaxies. These results hint at the presence of a large population of optically faint gas-rich dwarf galaxies, such as envisioned by Impey, Bothun & Malin (1988) and others.

A SEARCH FOR CLOSE DWARF COMPANIONS OF ELLIPTICAL GALAXIES

It is found that the mean number of dwarf companions within a projected distance of 75 kpc from e... more It is found that the mean number of dwarf companions within a projected distance of 75 kpc from each of a sample of 34 isolated giant elliptical galaxies is, in a statistical sense, +0.12 ± 0.42 (95% confidence interval). Comparison is made with the results of Holmberg (1969) for a similar survey of 115 spiral galaxies in which the mean number of dwarf companions was found to be 4-1.08 ± 0.37. We argue that these values differ by a significant amount and that differences in sample selection and other procedures would be likely, if anything, to increase the difference. Finally, we speculate on the possible reasons why elliptical galaxies have fewer, smaller, or intrinsically less luminous dwarf companions than spirals.

Ultraviolet Imaging Observations of the cD Galaxy in Abell 1795: Further Evidence for Massive Star Formation in a Cooling Flow

The Astrophysical Journal, 1997

We present images from the Ultraviolet Imaging Telescope of the Abell 1795 cluster of galaxies. W... more We present images from the Ultraviolet Imaging Telescope of the Abell 1795 cluster of galaxies. We compare the cD galaxy morphology and photometry of these data with those from existing archival and published data. The addition of a far-UV color helps us to construct and test star formation model scenarios for the sources of UV emission. Models of star formation with rates in the range ∼ 5 − 20M ⊙ yr −1 indicate that the best fitting models are those with continuous star formation or a recent (∼ 4 Myr old) burst superimposed on an old population. The presence of dust in the galaxy, dramatically revealed by HST images complicates the interpretation of UV data. However, we find that the broad-band UV/optical colors of this cD galaxy can be reasonably matched by models using a Galactic form for the extinction law with E B−V = 0.14. We also briefly discuss other objects in the large UIT field of view.

Bound populations around cD galaxies

The Arecibo Galaxy Environment Survey: precursor observations of the NGC 628 group

by Gregory Bothun, Noah Brosch, and Robert Minchin

The Arecibo Galaxy Environment Survey (AGES) is one of several H I surveys utilizing the new Arec... more The Arecibo Galaxy Environment Survey (AGES) is one of several H I surveys utilizing the new Arecibo L-band Feed Array (ALFA) fitted to the 305-m radio telescope at Arecibo. a The survey is specifically designed to investigate various galactic environments to higher sensitivity, higher velocity resolution and higher spatial resolution than previous fully sampled, 21-cm multibeam surveys. The emphasis is on making detailed observations of nearby objects although the large system bandwidth (100 MHz) will allow us to quantify the H I properties over a large instantaneous velocity range. In this paper, we describe the survey and its goals and present the results from the precursor observations of a 5 × 1-deg 2 region containing the nearby (∼10 Mpc) NGC 628 group. We have detected all the group galaxies in the region including the low-mass (M HI ∼10 7 M ⊙) dwarf, dw0137+1541. The fluxes and velocities for these galaxies compare well with previously published data. There is no intragroup neutral gas detected down to a limiting column density of 2 × 10 18 cm −2. In addition to the group galaxies we have detected 22 galaxies beyond the NGC 628 group, nine of which are previously uncatalogued. We present the H I data for these objects and also SuperCOSMOS images for possible optical galaxies that might be associated with the H I signal. We have used V/V max analysis to model how many galaxies beyond 1000 km s −1 should be detected and compare this with our results. The predicted number of detectable galaxies varies depending on the H I mass function (HIMF) used in the analysis. Unfortunately the precursor survey area is too small to determine whether this is saying anything fundamental about the HIMF or simply highlighting the effect of low number statistics. This is just one of many questions that will be addressed by the complete AGES survey.

EXTRAORDINARY DIFFUSE LIGHT IN HICKSON COMPACT GROUP 90

by Gregory Bothun and Wayne Barkhouse

A two-color photometric study is presented for the interacting compact system of galaxies Hickson... more A two-color photometric study is presented for the interacting compact system of galaxies Hickson Compact Group 90 (HCG 90). Currently, HCG 90's galaxies are experiencing a strong tidal interaction, and as a result, a significant luminous diffuse light component has formed. Through isophotal definition of the distinction between the galaxy light and diffuse intracluster light, approximately 38%–48% of the total light belongs to the diffuse light component. Moreover, the surface brightness of the '' tidal debris '' is much higher than seen in other interacting systems. The intracluster light has a narrow color distribution centered around a mean color of VÀR ¼ 0:67 AE 0:03 mag, which is consistent with an old stellar population. Although a spiral galaxy is heavily involved in an interaction, an associated blue component to the diffuse light is not clearly seen. An interaction of this magnitude would also remove much of the cold gas in the interacting galaxies, which would then be heated by the group potential; however, Chandra observations reveal only a very faint intracluster medium at energy of kT $ 0:7 keV. The X-ray–emitting gas shows a narrow bridge that connects two of the interacting galaxies. This morphology is similar to that exhibited by the diffuse optical emission. This morphology might be an indicator of a young dynamical age for this system. However, the overall lumi-nosity ratio of X-ray gas emission to the diffuse light emission is less than 10 À3 , and this might indicate a dynamical old system (e.g., the gas has cooled). Therefore, HCG 90 is a dynamical paradox in that it has a very large amount of diffuse intracluster light and a very small amount of related hot intracluster gas and has overall features that give conflicting inferences concerning its dynamical age.

A redshift survey of the poor cluster A1142

The Astronomical Journal, 1984

More bound populations around cD galaxies

The Astrophysical Journal, 1990

Nonlinearity of the Fully-Tisher relation

The Astrophysical Journal, 1989

The Baryonic Tully-Fisher Relation

We extend the Tully-Fisher relation over five decades in stellar mass using new data for dwarf lo... more We extend the Tully-Fisher relation over five decades in stellar mass using new data for dwarf low surface brightness galaxies. The data include many faint galaxies with masses as low as M* = 106 M&sun; and circular velocities as low as Vc = 40 km/s. We find a clear break in the optical-NIR Tully-Fisher relation: galaxies with Vc < 90 km/s fall systematically below the relation defined by brighter galaxies. These faint galaxies are however very gas rich; adding in the gas mass and plotting baryonic mass Mb = M* + Mgas in place of luminosity restores a single linear relation. The Tully-Fisher relation appears fundamentally to be a relation between rotation velocity and total baryonic mass. This work has been supported in part by NSF grants AST 84-08225, AST 87-18465, AST 99-01663 and NASA grants NGL 05002140 and NAGW 1710.

GOALS: The Great Observatories All-Sky LIRG Survey

by Gregory Bothun, Vassilis Charmandaris, and Joseph Jensen

The Great Observatories All-Sky LIRG Survey (GOALS 20) combines data from NASA's Spitzer Space Te... more The Great Observatories All-Sky LIRG Survey (GOALS 20) combines data from NASA's Spitzer Space Telescope, Chandra X-Ray Observatory, Hubble Space Telescope (HST), and Galaxy Evolution Explorer (GALEX) observatories, together with ground-based data, into a comprehensive imaging and spectroscopic survey of over 200 low-redshift (z < 0:088), Luminous Infrared Galaxies (LIRGs). The LIRGs are a complete subset of the IRAS Revised Bright Galaxy Sample (RBGS), which comprises 629 extragalactic objects with 60 μm flux densities above 5.24 Jy, and Galactic latitudes above five degrees. The LIRGs targeted in GOALS span the full range of nuclear spectral types defined via traditional optical line-ratio diagrams (type-1 and type-2 AGN, LINERs, and starbursts) as well as interaction stages (major mergers, minor mergers, and isolated galaxies). They provide an unbiased picture of the processes responsible for enhanced infrared emission in galaxies in the local Universe. As an example of the analytic power of the multiwavelength GOALS data set, we present Spitzer, Chandra, HST, and GALEX images and spectra for the interacting system VV 340 (IRAS F14547 þ 2449). The Spitzer MIPS imaging data indicates that between 80–95% of the total far-infrared emission (or about 5 × 10 11 L ⊙) originates in VV 340 north. While the Spitzer IRAC colors of VV 340 north and south are consistent with star-forming galaxies, both the Spitzer IRS and Chandra ACIS data indicate the presence of an AGN in VV 340 north. The observed line fluxes, without correction for extinction, imply that the AGN accounts for less than 10%–20% of the observed infrared emission. The X-ray data are consistent with a heavily absorbed (N H ≥ 10 24 cm À2) AGN. The GALEX far and near-UV fluxes imply a extremely large infrared " excess " (IRX) for the system (F IR =F fuv ∼ 81) which is well above the correlation seen in starburst galaxies. Most of this excess is driven by VV 340 N, which has an IR excess of nearly 400. The VV 340 system seems to be comprised of two very different galaxies: an infrared luminous edge-on galaxy (VV 340 north) that dominates the long-wavelength emission from the system, which hosts a buried AGN; and a face-on starburst (VV 340 south) that dominates the short-wavelength emission.

PECULIAR VELOCITIES FOR GALAXIES IN THE GREAT WALL. I. THE DATA

We construct the /-band Tully-Fisher relation (IRTF) for a sample of galaxies in the redshift spa... more We construct the /-band Tully-Fisher relation (IRTF) for a sample of galaxies in the redshift space vicinity of the Great Wall. We measure isophotal and total /-band magnitudes for the galaxies and use the Arecibo 305 m to obtain 20% and 50% linewidths for the galaxies. We construct TF relations from these data. The derived TF zero point for this relation is M 0 = —19.73, and the TF slope is ¿>=8.34, with scatter cr~0.30-0.32. We use the 20% linewidth relation for a study of the peculiar velocity field in a separate paper [Dell'Antonio et al 1996, ApJ, submitted (Paper II)]. We also investigate the effects of extinction on the IRTF. The data are consistent with a moderate internal extinction (Bothun et al 1992, ApJ, 395, 347), and are inconsistent with the strong internal extinction correction proposed by Bernstein et al (1994, AJ, 107, 1962).

Peculiar Velocities for Galaxies in the Great Wall II. Analysis

We analyze the peculiar velocity field in the vicinity of the Great Wall (GW) using a sample of 1... more We analyze the peculiar velocity field in the vicinity of the Great Wall (GW) using a sample of 172 spiral galaxies with reliable IRTF distance estimates (DelT Antonio et al. 1996). We examine three main issues: (1) the infall onto the GW, (2) large-scale flow, and (3) shear. We use a Monte Carlo method to remove selection-based biases from the peculiar velocity sample. For the GW sample, the velocity bias is small (^150 km s' 1). We use the bias-corrected velocities to constrain the infall towards the Great Wall. We thus have the first limits on the true spatial thickness of this structure. The data are best fit by an infall velocity ^150 km s " 1. The 90% upper limit on the mean infall velocity is —500 km s " 1. Consequently, the upper limit on the real-space full width of the GW is d<\\2h~ l Mpc. Thus, the Great Wall is a thin, two-dimensional structure in real space as well as in redshift space. We calculate the best-fit estimate of the motion of the Local Group with respect to the galaxy distribution: u flow ~725±400 km s' 1 towards a=11.7±1.5 hr, <5= 36.8° ±55°. Because our ô constraints are quite weak, this flow is consistent with the CMB dipole (Smoot et al 1992) and with the flow vector of Riess et al (1995). The data are also consistent at the 25% confidence level with the direction of large-scale flow reported by Lauer & Postman (1994). We calculate the improvement in sensitivity expected for a sample extending over the full declination range of the GW. We also calculate the shear across the right ascension range of the GW. The GW region is quiet: the detected the shear across the range of the GW is —70±210 km s' 1. The absence of large shear constrains the amplitude of large-scale density fluctuations (Feldman & Watkins 1995).

Eggen, Lynden-Bell & Sandage's Determination of the Galaxy's Collapse from Stellar Motions

$Research paper thumbnail of THE SPACE DENSITY OF GALAXIES THROUGH MAGNITUDES PER INVERSE k B (0) \ 25.0 ARCSECOND SQUARED$

THE SPACE DENSITY OF GALAXIES THROUGH MAGNITUDES PER INVERSE k B (0) \ 25.0 ARCSECOND SQUARED

Using the catalog of OÏNeil, Bothun, & Schombert, we examine the central surface brightness distr... more Using the catalog of OÏNeil, Bothun, & Schombert, we examine the central surface brightness distribution of galaxies in the mag arcsec~2 range. Taking advantage of having a (/[k B (0)]) 22.0 ¹ k B (0) ¹ 25.0 catalog in which each galaxy has a known central surface brightness, scale length, and redshift, we apply a bivariate volume correction to the data and extend the surface brightness distribution function by 1 magnitude, to 25.0 B mag arcsec~2. The result is a Ñat (slope \ 0) space density of galaxies as a function of from the Freeman value of 21.65 ^ 0.30 to the survey limit of 25.0 mag arcsec~2, more than 10 k B (0) p away. The galaxies that comprise this sample have scale lengths and circular velocities similar to L * spiral galaxies (i.e., these are not dwarf galaxies). As such, a signiÐcant amount of mass is contained in this population. If the baryonic mass fraction of disk galaxies is independent of then our results k B (0), are consistent with a signiÐcant percentage of the baryonic content of the universe being contained in potentials only dimly lit by the embedded galaxy.

STRUCTURAL CHARACTERISTICS OF FAINT GALAXIES SERENDIPITOUSLY DISCOVERED WITH THE HUBBL E SPACE T EL ESCOPE WFPC2 KAREN OÏNEIL1

Utilizing the F814W and F300W Ðlters, Hubble Space T elescope Wide Field Planetary Camera-2 (WFPC... more Utilizing the F814W and F300W Ðlters, Hubble Space T elescope Wide Field Planetary Camera-2 (WFPC2) images were taken of four low surface brightness galaxies in the direction of the Virgo ClusterÈV7L3, V2L8, V1L4, and Malin 1. The high resolution of the WFPC2 combined with the extremely di †use nature of the four galaxies makes them essentially transparent, allowing for the seren-dipitous discovery of 139 background galaxies visible through both the disks and nuclei of the foreground galaxies. Surface photometry was done on the newly discovered galaxies through the F814W (I-band) Ðlter. The detected galaxies have both r1@4 and exponential-type proÐles with radii (to the mag arcsec~2 limit) less than Their total magnitudes range from 18.9 through the k F814W \ 25.0 5A .0. survey cuto † at 25.0 in the F814W Ðlter. The median central surface brightness of those galaxies with exponential proÐles is approximately 1 mag brighter than the background F814W " " sky.ÏÏ Thus, with this data set we recover FreemanÏs law and hence know that we do not have a representative sample of distant galaxies (and neither does anyone else). When possible, the B, V , and I colors of these galaxies were determined using ground-based images, which show the galaxies to be fairly red. Coupled with their small angular size, we estimate the redshifts to be 0.5 ¹ z ¹ 1.5. ClassiÐcation of the galaxies was done strictly in structural terms, based only on the form of the derived luminosity proÐle. No morphological considerations were made during the classiÐcation process. Twenty-three percent of the galaxies we detected have the r1@4 proÐle typical of early-type galaxies, matching most previous studies of both the Hubble Deep Field and the Medium Deep Survey, which typically Ðnd 15%È40% E/S0 galaxies. In addition, we have attempted to perform bulge/disk deconvolu-tions. While we Ðnd that most of the sample cannot be easily deconvolved into a classic bulge]disk, seven objects could be Ðtted in this way. For these seven objects we Ðnd (1) a large range in bulge-to-total luminosity and (2) some disks that have a large bulge-to-disk ratio. We also present one object, 283-10, which is an excellent example of the structural ambiguity that exists in the luminosity proÐles of distant galaxies. In agreement with other studies, we also found a signiÐcant percentage of galaxies that have disturbed luminosity proÐles indicative of probable galaxy-galaxy interactions or mergers. Indirect indicators suggest that the volume over which r1@4 objects are selected is signiÐcantly larger than the volume over which disk galaxies are selected. This implies a relatively low space density of r1@4 at all redshifts out to z D 2.5 and is consistent with the general idea that r1@4 galaxies are largely conÐned to galaxy clusters.

Diffuse Baryons in the Universe: Galaxies, Warm Gas, or Cold Lonely Lumps

Astrophysics and Space Science Library, 2003

ABSTRACT

Precision cosmological measurements: Independent evidence for dark energy

Physics Letters B, 2008

Using recent precision measurements of cosmological paramters, we re-examine whether these observ... more Using recent precision measurements of cosmological paramters, we re-examine whether these observations alone, independent of type Ia supernova surveys, are sufficient to imply the existence of dark energy. We find that best measurements of the age of the universe t0, the Hubble parameter H0 and the matter fraction Ωm strongly favor an equation of state defined by (w < −1/3). This result is consistent with the existence of a repulsive, acceleration-causing component of energy if the universe is nearly flat.

Structural Characteristics of Faint Galaxies Serendipitously Discovered with the HST WFPC2

[Abridged] HST WFPC2 images were taken of four low surface brightness galaxies in the direction o... more [Abridged] HST WFPC2 images were taken of four low surface brightness galaxies in the direction of the Virgo cluster. The high resolution of the WFPC2 combined with the extremely diffuse nature of the four galaxies makes them essentially transparent, allowing for the serendipitous discovery of 139 background galaxies visible through both the disks and nuclei of the foreground galaxies. Surface photometry was done on the newly discovered galaxies through the F814W (I-band) filter, showing the median central surface brightness of those galaxies with exponential profiles is approximately one magnitude brighter than the background F814W "sky". Thus, with this dataset we recover Freeman's law and hence know that we do not have a representative sample of distant galaxies (and neither does anyone else). Classification of the galaxies was done strictly in structural terms, based only on the form of the derived luminosity profile. No morphological considerations were made during the classification process. 23% of the galaxies we detected have the r^{1/4} profile typical of early type galaxies, matching most previous studies of both the Hubble Deep Field and the Medium Deep Survey which typically find 15% - 40% E/S0 galaxies. In agreement with other studies we also found a significant percentage of galaxies which have disturbed luminosity profiles indicative of probable galaxy-galaxy interactions or mergers. Indirect indicators suggest that the volume over which r^{1/4} objects are selected is significantly larger than the volume over which disk galaxies are selected. This implies a relatively low space density of r^{1/4} at all redshifts out to z ~ 2.5 and is consistent with the general idea that r^{1/4} galaxies are largely confined to galaxy clusters.

$Research paper thumbnail of The Space Density of Galaxies through mu_B(0) = 25.0 mag arcsec^{-2}$

The Space Density of Galaxies through mu_B(0) = 25.0 mag arcsec^{-2}

Eprint Arxiv Astro Ph 9909123, Sep 7, 1999

Using the catalog of O'Neil, Bothun, & Schombert (1999), we examine the central surface brightnes... more Using the catalog of O'Neil, Bothun, & Schombert (1999), we examine the central surface brightness distribution (phi(mu_B(0))) of galaxies in the 22.0 < mu_B(0) < 25.0 mag arcsec^{-2} range. Taking advantage of having a catalog in which each galaxy has a known central surface brightness, scale length, and redshift, we apply a bi-variate volume correction to the data and extend the surface brightness distribution function by one magnitude, to 25.0 B mag arcsec^{-2}. The result is a flat (slope = 0) surface brightness distribution function from the Freeman value of 21.65 +/- 0.30 to the survey limit of 25.0 mag arcsec^{-2}, more than 11 sigma away. This indicates that a significant percentage of the baryonic content of the universe is likely in potentials only dimly lit by the embedded galaxy.

The Space Density of Galaxies in the Local Universe

Using the catalog of O'Neil, Bothun, & Schombert (1999), we examine the central surface brightnes... more Using the catalog of O'Neil, Bothun, & Schombert (1999), we examine the central surface brightness distribution (φ (μ B(0))) of galaxies in the 22.0 <= μ B(0) <= 25.0 mag arcsec-2 range. Taking advantage of having a catalog in which each galaxy has a known central surface brightness, scale length, and redshift, we apply a bi-variate volume correction to the data and extend the surface brightness distribution function by one magnitude, to 25.0 B mag arcsec-2. The result is a flat (slope = 0) surface brightness distribution function from the Freeman value of 21.65 +/- 0.30 to the survey limit of 25.0 mag arcsec-2, more than 11σ away. This indicates that a significant percentage of the baryonic content of the universe is likely in potentials only dimly lit by the embedded galaxy.

Stellar populations and the white dwarf mass function: Connections to supernova IA luminosities

The Astronomical Journal, 1997

We discuss the luminosity function of SNe Ia under the assumption that recent evidence for disper... more We discuss the luminosity function of SNe Ia under the assumption that recent evidence for dispersion in this standard candle is related to variations in the white dwarf mass function (WDMF) in the host galaxies. We develop a simple parameterization of the WDMF as a function of age of a stellar population and apply this to galaxies of different morphological types. We show that this simplified model is consistent with the observed WDMF of for the solar neighborhood. Our simple models predict that WDMF variations can produce a range of more than 1. m 8 in M B (SN Ia), which is comparable to the observed value using the data of Phillips (1993) and . We also predict a galaxy type dependence of M B (SN Ia) under standard assumptions of the star formation history in these galaxies and show that M B (SN Ia) can evolve with redshift. In principle both evolutionary and galaxy type corrections should be applied to recover the intrinsic range of M B (SN Ia) from the observed values. Our current inadequate knowledge of the star formation history of galaxies coupled with poor physical understanding of the SN Ia mechanism makes the reliable estimation of these corrections both difficult and controversial. The predictions of our models combined with the observed galaxy and redshift correlations may have the power to discriminate between the Chandrasekhar and the sub-Chandrasekhar progenitor scenarios for SNe Ia.

Optical observations of SN 1987D in UGC 7370

Publications of the Astronomical Society of the Pacific, 1987

Peculiar velocities of field spiral galaxies near and beyond the Great Attractor

The Astrophysical Journal, 1992

The velocity-distance relation for galaxies on a bubble

The Astrophysical Journal, Sep 20, 1992

The characteristic diameter of the most prominent void in the redshift survey of de Lapparent et ... more The characteristic diameter of the most prominent void in the redshift survey of de Lapparent et al. (1986) is measured. Distances and peculiar velocities to individual galaxies are derived, and it is shown that the void is approximately a 'Hubble Bubble' in which the near and far edges are separating with the general expansion of the universe. At the 3 sigma level, infall toward the Coma cluster is detected for a portion of the bubble wall. Limits on the net outflow from the void and infall into Coma are used to estimate Omega.

Searching for Infall on the Back of the Great Attractor: The Flow Continues

Deviations from the Fundamental Plane and the Peculiar Velocities of Clusters

The Astronomical Journal, 2001

We have fit the Fundamental Plane of Ellipticals (FP) to over 400 early-type galaxies in 20 nearb... more We have fit the Fundamental Plane of Ellipticals (FP) to over 400 early-type galaxies in 20 nearby clusters (cz ∼ 4000 − 11000 km s −1 ), using our own photometry and spectroscopy as well as measurements culled from the literature. We find that the quality-of-fit, r.m.s.[log(σ)], to the average Fundamental Plane (FP) varies substantially among these clusters. A statistically significant gap in r.m.s.[log(σ)] roughly separates the clusters which fit FP well from those that do not.

Emission-line galaxies in the Slice of the Universe

The Astronomical Journal, 1988

Deviations from the Fundamental Plane and Implications for Cluster Peculiar Velocities

We have fit the fundamental plane (FP) to elliptical galaxies in 20 nearby clusters (cz ~ 4000-11... more We have fit the fundamental plane (FP) to elliptical galaxies in 20 nearby clusters (cz ~ 4000-11000 km s(-1) ), using our own photometry and spectroscopy as well as measurements culled from the literature. We find that the goodness-of-fit to an average fundamental plane (/line{FP}) varies by more than a factor of two between these clusters. The sample is distinctly bimodal in r.m.s.;: about half the clusters fit the /line{FP} well, 0.05 < r.m.s.[log(sigma )]< 0.06, while the rest do not, 0.08 < r.m.s.[log(sigma )]< 0.11. The clusters with low scatter about the /line{FP} are found to be at rest with respect to the cosmic microwave background (CMB) within our measurement errors ( ~ 250 km s(-1) ). Only poor-fit clusters show large peculiar velocities (PV's), implying inaccurate measurement, rather than true indications of large peculiar motions. Furthermore, we find that all x-ray bright clusters in our sample fit the /line{FP} well, suggesting that in the most massive, virialized clusters the ellipticals form a more uniform sample.

ROSAT OBSERVATIONS OF QUIESCENT LOW MASS DISK GALAXIES: NO EVIDENCE OF BARYONIC BLOW OUT

To test the hypothesis that galactic winds associated with star formation in low mass disk galaxi... more To test the hypothesis that galactic winds associated with star formation in low mass disk galaxies can be an effective means of relocating cold disk gas to a warm tenuous halo, we have obtained long exposure ROSAT PSPC observations of three such galaxies. The sensitivity of the PSPC to the presence of an extended, approximately 0.15 KEY halo of 10 9 ^ o °f g as > is hi g h for the exposure times we used. We failed to detect this halo in all three cases and the observed x-ray luminosity of the galaxy is two orders of magnitude less than the hypothetical case in which the mass of gas that has been expelled by previous generations of star formation is equal to the stellar mass of the galaxy itself. This limit is much less than the actual mass of cold gas in these galaxies. Thus, we were unable to verify directly the presence of significant galactic winds in these three galaxies either because they are not operative, because their halos are not sufficiently massive to aid in the retention of this gas, or because the amount of injected gas is just a small percentage of the cold disk gas. If the latter reason is emblematic of low mass galaxies then we would not expect the detection of halos. We also report here the serendipitous detection of Abell 1560, a distance class 7 cluster of unknown redshift.

Carbon Stars at High Galactic Latitude

Photometry and kinematics are presented for a sample of objective prism selected carbon stars tow... more Photometry and kinematics are presented for a sample of objective prism selected carbon stars towards the north and south Galactic poles. Distances are determined by fitting the infrared colors to a giant branch. If these stars are like the carbon stars seen in dwarf spheroidal galaxies, the median distance of the sample is 28 kpc. If they are more like the carbon stars found recently in the Galactic bulge, they may be only half as distant. The surface density of carbon stars as a function of distance is remarkably consistent with an R 1/4 density profile for the Galactic halo. This density profile can be traced to ^ 15 scale radii and fills a volume similar to that occupied by globular clusters. The data yield an effective radius of either 7.0 or 3.5 kpc depending on choice of distance scale. The velocity dispersion of the sample is 96 + 12 km/s. A kinematic model in which vertical velocity dispersion is independent of height above the Galactic plane seems in best accord with the data.

5. The X-Ray and Optical Characteristics of the Cataclysmic Variable V794 Aql

The Peculiar X-ray and radio star AS431

The Zwicky Magnitude Scale: How Reliable is it in the Estimation of Blue Luminosity?

Tracing Polycyclic Aromatic Hydrocarbons and Warm Dust Emission in the Seyfert Galaxy NGC 1068

The Astronomical Journal, 2007

We present a study of the nearby Seyfert galaxy NGC 1068 using mid-and farinfrared data acquired ... more We present a study of the nearby Seyfert galaxy NGC 1068 using mid-and farinfrared data acquired with the IRAC, IRS, and MIPS instruments aboard the Spitzer Space Telescope. The images show extensive 8 µm and 24 µm emission coinciding with star formation in the inner spiral approximately 15 ′′ (1 kpc) from the nucleus, and a bright complex of star formation ∼47 ′′ (3 kpc) SW of the nucleus. The brightest 8 µm PAH emission regions coincide remarkably well with knots observed in an Hα image. Strong PAH features at 6.2, 7.7, 8.6, and 11.3 µm are detected in IRS spectra measured at numerous locations inside,

THE SPATIAL EXTENT OF (U)LIRGs IN THE MID-INFRARED. I. THE CONTINUUM EMISSION

We present an analysis of the extended mid-infrared (MIR) emission of the Great Observatories All... more We present an analysis of the extended mid-infrared (MIR) emission of the Great Observatories All-Sky LIRG Survey (GOALS) sample based on 5 − 15 µm low resolution spectra obtained with the Infrared Spectrograph on Spitzer. We calculate the fraction of extended emission as a function of wavelength for the galaxies in the sample, F EE λ , defined as the fraction of the emission which originates outside of the unresolved component of a source at a given distance. We find that the F EE λ varies from one galaxy to another, but we can identify three general types of F EE λ : one where F EE λ is constant, one where features due to emission lines and polycyclic aromatic hydrocarbons (PAH) appear more extended than the continuum, and a third which is characteristic of sources with deep silicate absorption at 9.7 µm. More than 30% of the galaxies have a median F EE λ larger than 0.5, implying that at least half of their MIR emission is extended. Luminous Infrared Galaxies (LIRGs) display a wide range of F EE in their warm dust continuum (0 F EE 13.2µm 0.85). The large values of F EE 13.2µm that we find in many LIRGs suggest that the extended component of their MIR continuum emission originates in scales up to 10 kpc, and may contribute as much as the nuclear region to their total MIR luminosity. The mean size of the LIRG cores at 13.2 µm is 2.6 kpc. However, once the IR luminosity of the systems reaches the threshold of L IR ∼ 10 11.8 L ⊙ , slightly below the regime of Ultra-luminous Infrared Galaxies (ULIRGs), all sources become clearly more compact, with F EE 13.2µm 0.2, and their cores are unresolved. Our estimated upper limit for the core size of ULIRGs is less than 1.5 kpc. Furthermore, our analysis indicates that the compactness of systems with L IR 10 11.25 L ⊙ strongly increases in those classified as mergers in their final stage of interaction. The F EE 13.2µm is also related to the contribution of an active galactic nucleus (AGN) to the MIR emission. Galaxies which are more AGN-dominated are less extended, independently of their L IR . We finally find that the extent of the MIR continuum emission is correlated with the far-IR IRAS log(f 60 µm /f 100 µm ) color. This enables us to place a lower limit to the area in a galaxy from where the cold dust emission may originate, a prediction which can be tested soon with the Herschel Space Telescope.

A fast focal-reducing camera for CCD imaging

Publications of the Astronomical Society of the Pacific, 1991

The faint end of the Zwicky magnitude scale - CCD isophotal magnitudes versus Zwicky magnitudes

The Astronomical Journal, 1990

A method for obtaining the age and scale height of the thick disk from faint Stromgren photometry

The Astrophysical Journal, 1993

The New Michigan Focal Reducing Camera

An Unsuccessful Search for Very Extended Halos Around NGC 1300 and M61

We have undertaken a sensitive search for H and Κ absorption arising in the halos of two spiral g... more We have undertaken a sensitive search for H and Κ absorption arising in the halos of two spiral galaxies that are projected against background QSOs, using a blue-sensitive spectrograph attached to the Multiple Mirror Telescope (MMT). Despite good sensitivity (S/iV ~ 20) and high spectral resolution (1 Â), this search program produced a null result. In our best case, we can set an upper limit on the equivalent width of Η and Κ absorption of 0.1 Á. A 21-cm search for a very extended halo around NGC 1300 was also negative, restricting ΗI emission column densities to < 10 20 cm-2 at distances > 50 kpc from the nucleus.

Schimmen aan de nachthemel

Our universe: the thrill of extragalactic exploration as told by leading experts

... New York, NY 10011-4211, USA 10 Stamford Road, Oakleigh, VIC 3166, Australia Ruiz de Alarcon ... more

Halpha and [NII] Emission in Isolated Early-Type Galaxies

Book Review: Modern cosmological observations and problems / Taylor & Francis, 1998

Space Sci Rev, 1998

HCG 90: the Formation of the X-Ray Medium?

Chandra Proposal, Sep 1, 1999

At optical wavelengths Hickson Compact Group 90 exhibits an unprecedented amount of diffuse intra... more At optical wavelengths Hickson Compact Group 90 exhibits an unprecedented amount of diffuse intracluster light whose total luminosity is approximately 40% of the group luminosity. Three luminous galaxies, including the hard X-ray source NGC 7172, are currently strongly interacting and merging, producing a substantial amount of tidal debris which comprises the intracluster light. Previous ROSAT HRI observations of HCG 90 hint at the presence of weak, diffuse X-ray emission. We propose to use the AXAF ACIS detector to acquire better data to confirm that HCG 90 has an extended region of X-ray emission with very low value of L_x/L_opt indicating that the ICM in this group is just now in the process of forming and heating as a direct response to strong galaxy-galaxy interactions.

Globular Clusters in Different Types of Spiral Galaxies

Proceedings of the International Astronomical Union, 1988

The authors have identified (or set upper limits on) the cluster systems in several edge-on spira... more

Globular Clusters in Spiral Galaxies

Abell 1367 HI sources from AGES (Cortese+, 2008)

As part of the AGES, we observed the Abell 1367 region in 2006 May and 2007 April using the ALFA ... more

Real Data Driven JAVA Applets for Astronomy Education

We describe our progress to date on the construction of highly interactive applets based on real ... more We describe our progress to date on the construction of highly interactive applets based on real data for use in elementary and advanced astronomy classes. In the current climate, there is wholesale resistance and skepticism involving applet usage as a standard part of the curriculum. The reasons for this are many and varied but at least partially flow from a lack of knowing what is available and what is possible. In this talk, we hope to demonstrate some sophisticated and robust applets whose activities can not be reproduced by standard canned exercises and whose framework allows the ability for students to work together in teams on larger scale homework problems. The use of such material adds a dimension to Astronomy 101 that hitherto does not exist, particularly in large classes. The purpose of this talk is to make the community aware that such resources now exist. This work is supported by NSF grant DUE-9752384 and also by the NSF's Recognition Award for the Integration of Research into Education.

A New Member of the Local Group?

An August 2002 detection at 21-cm of a previously undetected low surface brightness galaxy yielde... more An August 2002 detection at 21-cm of a previously undetected low surface brightness galaxy yielded a radial velocity of -360 km/s. As the galaxy is located in the opposite part of the sky as the Virgo cluster, its seems quite likely that this velocity places it squarely in the Local Group {LG}. The characteristics of this galaxy, if its at a distance of 1-2 Mpc, are such that it easily could have escaped detection from previous searches. Its optical surface brightness is low and its integrated blue magnitude would lie in the range -6.5 to -8.0. The total H I mass is less than 3 x 10^5 solar masses. The H I profile is relatively low S/N and distorted, with a signal that is spread out over about 80 km/s. much larger than the internal velocity dispersion of the galaxy. This is likely the result of an interaction {most probably with M31}. With the efficiency of the ACS, we can easily detect the TRGB population in this object using V and I observations in 2 orbits. The goal here is to provide confirming evidence that this object is indeed a member of the LG by obtaining its distance via the now well calibrtated TRGB method using V-I as the filter system. If indeed in the LG {which seems likely} it would also represent a new kind of dwarf galaxy as its considerably more compact than other LG dwarfs of similar absolute magnitude.

Narrow band images of suspected cooling flow galaxies

Narrow-band (H alpha and (NII)) charge coupled device (CCD) images of elliptical galaxies suspect... more Narrow-band (H alpha and (NII)) charge coupled device (CCD) images of elliptical galaxies suspected of having cooling flows are discussed. Researchers find evidence of optical emission from cool gas which is most likely associated with a cooling flow. At least 4 galaxies (NGC 3998, NGC 4203, NGC 4550 and NGC 4697) show emission of (NII) and/or H alpha within the central 20 seconds, a fraction consistent with results from Phillips et al. (1987) and Caldwell (1984). In these four, (NII) lambda 6584A emission is stronger than H alpha (which is often in absorption e.g., as seen in long slit spectra of NGC4697). From long slit spectra of these galaxies, Deustua and Teske (1989) infer electron densities, Ne, of order 1.2x10 to the 3rd power cm(-3) assuming T = 10 to the 4th power K for the optically emitting gas. NGC 2685, NGC 3489 appear to have emission in (NII); NGC 4636 may also, but, is difficult to see in the data (Demoulin-Ulrich, Butcher and Boksenberg (1984) did not see emission from this galaxy). NGC 4472, NGC 4473, NGC 4365, NGC 4638 and NGC 4649 show no emission.

Do Galaxy Disks Ever Really End?

We have been engaged in a ground based U-band survey of a sample of very large scale length (> 5 ... more We have been engaged in a ground based U-band survey of a sample of very large scale length (> 5 kpc), relatively isolated, face-on disk galaxies that exhibit strong spiral structure, in order to identify potential candidates like the remarkable galaxy NGC 300, which has recently been shown to exhibit a continuous exponential disk over 6-10 optical scale lengths. Our U-band data shows coherent exponential disks over 4-5 scale lengths and we seek to use the excellent power of GALEX in detecting low surface brightness stellar populations to better show the true extent of these disks, The detection of such extended stellar distributions would provide strong confirmation that a) star formation does occur in very low surface density environments, b) disk galaxies have dynamical continuity that exceeds that which can currently be understood theoretically and c) such extended environments are the parent population of intergalactic stars/baryonic debris as these environments are disrupted through hierarchical clustering processes. If the NGC 300 phenomena can be shown to exist in other structures then this represents a profound theoretical challenge to both our understanding of disk galaxy formation and assembling as well as star formation. Two added bonuses of these observations are 1) the discovery of another laboratory to potentially study the dynamics of objects located in a very low gravitational acceleration environment and 2) obtaining NUV morphologies of very large disk galaxies, (which are likely the objects most easily detected at high redshift) at the same rest frame stellar population light as high redshift disks. Convolving the images to the same physical resolution would then allow for a direct comparison of galaxy morphology in large disk galaxies at z=1 compared to z=0.."

The Velocity Fields of Cluster Spirals

Nonlinearity of the Tully-Fisher relation. [Dark matter in spiral galaxies]

ABSTRACT

IRAS observations of optically selected galaxies. I - The properties of the UGC redshift sample

The Astrophysical Journal, 1989

Teaching with Electrons: The Good, The Bad, and the Ugly

Aps March Meeting Abstracts, Mar 1, 2000

The World Wide Web went from obscurity to production over just a two year period (1994-1996). We ... more The World Wide Web went from obscurity to production over just a two year period (1994-1996). We are well into the production aspect of the Web and should, by now, be using it to its full potential as an educational tool that significantly improves the way in which introductory physics can be taught. At the University of Oregon we have been quite active in the use of JAVA based interactive modules which allow for virtual experimentation and simulation and have developed a suite of tools to facilitate group data acquisition, reduction and management. Every possible failure mode has been encountered along the way. Student and faculty resistance has also been acute. As a result, we are in a good position to comment on the overall value and usefulness of this approach. We find that despite all the potential problems, the outcomes are significant and introductory students become engaged in a whole new way of learning.

Using JAVA Tools to Promote Student Collaborative Projects

The Mass-To-Light Ratios of Low Surface Brightness Galaxies

We have obtained 21-cm profiles and I or R band surface photometry for a subset of field low surf... more We have obtained 21-cm profiles and I or R band surface photometry for a subset of field low surface brightness (LSB) galaxies from the survey presented elsewhere at this meeting by Impey et al. We find that, in comparison to higher surface brightness (HSB) galaxies, a subset of the LSB galaxies are significantly underluminous for their rotation speeds. The LSB galaxies are bluer than the HSB galaxies, which suggests that they have different stellar populations. However, the population differences cannot account for the difference in M/L ratios implied by the deviation from the normal Tully-Fisher relation. The most plausible explanation is that this subset of field LSB galaxies have higher dark-to-luminous matter ratios than do HSB galaxies, a result that is consistent with previous work on LSB dwarf galaxies in the Local Group and in the Virgo and Fornax clusters. Contamination by such underluminous galaxies may account for some of the high peculiar velocities found in previous surveys using the Tully-Fisher relation as a distance indicator.

Low Surface Brightness Galaxies in the Local Universe

Bulletin of the American Astronomical Society, 1993

A large new survey of low surface brightness galaxies is reported, based on manual and automated ... more A large new survey of low surface brightness galaxies is reported, based on manual and automated scans of plates from the UK Schmidt Telescope in a strip of sky centered on the equator. We find 518 previously cataloged galaxies in 792 square degrees. The survey is complete to angular sizes of roughly 20 arcseconds at the 26 B mag per square arcsecond isophote. Redshifts have been obtained for 2/3 of the sample using optical spectroscopy at the MMT and HI measurements at Arecibo. CCD surface photometry in the B,V, and R bands has been obtained for a morphologically representative subset. The median redshift is about 9000 km/s. Low surface brightness galaxies have been systematically excluded from almost every published catalog of galaxies. This new sample is being used to adress several issues, including the form of the galaxy luminosity function when corrected for surface brightness selection effects, the large scale clustering of diffuse stellar systems, and the nature of the faint blue galaxies seen in deep pencil beam surveys.

Low Surface Brightness Galaxies

Annual Review of Astronomy and Astrophysics, 1997

The properties of galaxies that are lower in surface brightness than the dark night sky are revie... more The properties of galaxies that are lower in surface brightness than the dark night sky are reviewed. There are substantial selection effects against the discovery of galaxies that are unevolved or diffuse; these systems are missing from most wide field catalogs. Low surface brightness galaxies make up a significant amount of the luminosity density of the local universe. They contribute substantial but poorly determined amounts to the census of baryons and dark matter. Low surface brightness galaxies are also relevant to the interpretation of quasar absorption lines and to the understanding of rapidly evolving galaxy populations in the more distant universe. Theories of galaxy formation and evolution must accomodate the properties of these diffuse stellar systems.

HST photometry of 4 Virgo LSB galaxies (O'Neil+, 2000)

Utilizing the F814W and F300W filters, Hubble Space Telescope Wide Field Planetary Camera-2 (WFPC... more Utilizing the F814W and F300W filters, Hubble Space Telescope Wide Field Planetary Camera-2 (WFPC2) images were taken of four low surface brightness galaxies in the direction of the Virgo Cluster - V7L3, V2L8, V1L4, and Malin 1. The high resolution of the WFPC2 combined with the extremely diffuse nature of the four galaxies makes them essentially transparent, allowing for the serendipitous discovery of 139 background galaxies visible through both the disks and nuclei of the foreground galaxies. Surface photometry was done on the newly discovered galaxies through the F814W (I-band) filter. The detected galaxies have both r1/4 and exponential-type profiles with radii (to the μF814W=25.0mag/arcsec2 limit) less than 5.0". Their total magnitudes range from 18.9 through the survey cutoff at 25.0 in the F814W filter. (3 data files).

IR Photometry of SO Disks: Evidence for Intermediate Age Disk Populations

U8508 - A Dwarf Galaxy Associated with the M101 Group

Globular cluster populations of Hickson compact groups

We present deep V and R band CCD photometry of the globular cluster systems of Hickson compact gr... more We present deep V and R band CCD photometry of the globular cluster systems of Hickson compact group galaxy 22a (NGC 1199) and 90c (NGC 7173), taken with the European Southern Observatory's New Technology Telescope (NTT). Globular cluster populations were detected in both galaxies, with HCG 22a having a specific frequency of SN ~ 2 and HCG 90c having a value of SN ~ 4. Both values of specific frequency are consistent with the average value found for field ellipticals. These results give rise to two possible scenarios for globular cluster formation in these galaxies; a) globular clusters formed during the time when their parent galaxy was simply a 'field` galaxy, or b) mergers are not important in the formation of globular clusters in Hickson compact groups (Hickson compact groups are expected to have high merger rates due to their large densities and low velocity dispersions).

The Intrinsic Structure and Color of IC 342 from CCD Observations

We have reobserved the nearby galaxy IC 342 through U, B, and I filters using a CCD system with a... more We have reobserved the nearby galaxy IC 342 through U, B, and I filters using a CCD system with a sufficiently large field of view that the entire galaxy can be imaged in one exposure. Our purpose is to better quantify the optical structure of IC 342 on the basis of modern detectors. Through a combination of surface photometry and grid photometry, we have extracted structural parameters and color distributions for IC 342. We conclude that (1) the scale length of the underlying light distribution is approximately , (2) little 250 10 evidence for significant reddening variations is observed across the face of IC 342, and (3) consistency between the disk and/or spiral arm component of IC 342 compared to other Sc galaxies is best obtained with a foreground reddening value of , significantly lower than most other recent estimates (which are as high as). A ∼ 2.0 A ∼ 3.3 b b

The dependence of H II region properties on global and local surface brightness within galaxy discs

Using B, R and Hα images of roughly equal-sized samples of low surface brightness (LSB) and high ... more Using B, R and Hα images of roughly equal-sized samples of low surface brightness (LSB) and high surface brightness (HSB) galaxies (∼40 galaxies apiece), we have explored the dependence of H II region properties on local and global disc surface brightness. We have done this by constructing co-added H II region luminosity functions (LFs) according to local and central disc surface brightness and fitting Schechter functions to these LFs. The results show that the shape of the H II region LF within LSB galaxies does not change noticeably as different limiting (i.e. μ > μ lim) local surface brightness values are used. However, the LFs for HSB galaxies have larger values of L * and are less steep at the faint-end than those of LSB galaxies for limiting B-band local surface brightness values as faint as μ B,lim 23– 24. Both the LFs and the data for individual H II regions show that luminous (L > 10 39 erg s −1) H II regions are much more common within HSB discs than within LSB discs, implying that the newly formed star clusters are also larger. Taking this into account along with the results of Monte Carlo simulations, the shapes of the LFs imply that the regions within LSB discs and those within the LSB areas of HSB discs are relatively old (∼5 Myr) while the regions within HSB discs for μ B 24 are significantly younger (<1 Myr). Since the majority of the LSB galaxies do not have noticeable spiral arms and the majority of the HSB galaxies do, this may indicate a transition within HSB discs from spiral arm-driven star formation to a more locally driven, possibly sporadic form of star formation at μ B ∼ 24, a transition that does not appear to occur within LSB discs.

VLA observations of the giant cluster spiral UGC 12423

The Astronomical Journal, 1982

Peculiar velocities in large-scale structure - The problem of incomplete sampling

The Astrophysical Journal, 1990

HUBBL E SPACE T EL ESCOPE WFPC2 IMAGING OF THREE LOW SURFACE BRIGHTNESS DWARF ELLIPTICAL GALAXIES IN THE VIRGO CLUSTER KAREN OÏNEIL1

Utilizing the F814W and F300W Ðlters, Hubble Space T elescope Wide Field Planetary Camera 2 (WFPC... more Utilizing the F814W and F300W Ðlters, Hubble Space T elescope Wide Field Planetary Camera 2 (WFPC2) images were taken of three low surface brightness dwarf elliptical galaxies in the Virgo Cluster. The intent of the observations was to determine the small-scale structure in these enigmatic galaxies and to attempt to learn something about the nature of their giant branches through the detection of lumi-nosity Ñuctuations. In two of the three studied galaxies, V7L3 and V1L4, the luminosity Ñuctuations in the inner, constant surface brightness regions were unambiguously detected. At the nominal distance of the Virgo Cluster, the measured luminosity Ñuctuations in the F814W band yields a density of 2È10 red giants per pixel. In the most extreme of these two cases, V7L3, we derive a surface density of giant stars of D3 per 10 pc2. Using the observed B[V and V [I colors as a constraint, we could Ðnd no model that would reproduce the observed Ñuctuation signal and blue colors if there were a signiÐcant population of M giants in these systems. Overall, our results are consistent with a mean spectral type of K0ÈK2, which implies a relatively metal-poor population. The third system, V2L8, did not have a detectable Ñuctuation signal, which possibly implies that it is not in the Virgo Cluster. Interestingly, this system is highly nucleated. Our observations have resolved this nucleus, and if V2L8 is in Virgo, then we have discovered what is likely the smallest bulge measured to date, having an e †ective radius of only 50 pc. This bulge is quite red (as red as giant ellipticals), and it is entirely possible that this nucleated dwarf elliptical galaxy, in fact, is a very large galaxy located in the background. As such, it is highly reminiscent of the manner in which Malin 1 was discovered. Optical spectroscopy of this nucleus is required to conÐrm this. Finally, we Ðnd no evidence for small-scale clumping of stars in any of the studied systems at this much-improved spatial resolution. This implies that these systems are dynamically well relaxed and that the physical cause of their observed low surface brightnesses is their low density. When imaged at the high spatial resolution of the WFPC2 (D6 pc pixel~1), the galaxies are easy to look right through without even knowing that they are present in the very middle of the WFPC2 frame. They appear only as elevated " " sky noise. ÏÏ

Detection of the Globular Cluster Population Around NGC 7814

We report the statistical detection of 120 ±25 globular clusters in fields surrounding the edge-o... more We report the statistical detection of 120 ±25 globular clusters in fields surrounding the edge-on S0 3 galaxy NGC 7814. Counts of objects are made to F=24.5 and reach at least the peak of the globular-cluster luminosity function (GCLF). The bulge of NGC 7814 is of moderate luminosity and is highly flattened with an axial ratio of 6/0=0.48. Counts made from 0!5-5!0 radius in concentric rings of width 0!5 show a clear detection of excess objects relative to the background in each annulus. Correcting for incompleteness in both magnitude and areal coverage yields a total cluster population of 498 ± 164 within this region. We are thus confident that we have a strong detection of the globular-cluster system (GCS) of NGC 7814. Accounting for the presence of clusters that we could not detect in the inner few kpc and those that might lie outside our survey area would likely increase the total population by a factor of 2. At our assumed distance of (m—Af) = 30.48, the specific frequency (5) of globulars is 7.6 ±3.2. The intrinsic GCLF for NGC 7814 is very poorly determined from these data but may indicate a distance 1 mag further away, in which case S would be 5.2 ±2.2. These values of .S are typical for elliptical galaxies but are rather high compared to those of spirals. The radial distribution of globular-cluster candidates does not fall off as fast as the halo light. Excess counts in a field not centered on the minor axis can only be reconciled with the rest of the data if the GCS of NGC 7814 is highly flattened.

Neutral hydrogen profiles of cluster galaxies

The Astrophysical Journal Supplement Series, 1995

H I absorption in the peculiar galaxy UGC 6081

The Astrophysical Journal, 1983

Peculiar Velocities for Galaxies in the Great Wall.I.The Data

The Astronomical Journal, 1996

... OO~6 OOO~ OOSØ OOO~ OOSL OD~ ~9i.ZsP!I &~r~ 0I 330 ~ 0001 OOSL OOO~ OOSQ ooo~ oocc DOOS f... more

DEEP UV IMAGING OF GALAXIES IN THE FORNAX CLUSTER

We compare the Astro-1 Ultraviolet Imaging Telescope (UIT) deep image of the Fornax cluster with ... more We compare the Astro-1 Ultraviolet Imaging Telescope (UIT) deep image of the Fornax cluster with deep optical surveys for purposes of determining the efficacy of vacuum ultraviolet imaging in terms of the recovery of very faint and/or diffuse galaxies. This field covers approximately 1/3 of a square degree and contains 15 galaxies with B t brighter than 18.0 mag. A 1000 s near-UV image detected ten of these galaxies. These ten detections include three luminous ellipticals, two bonafide dwarf ellipticals, and five galaxies of small angular size that may or may not be members of the Fornax cluster. If these optically faint galaxies are members of the Fornax cluster, then the VUV imaging did sample an appreciable range in the galaxy luminosity function. For the dwarf ellipticals, a comparison of their optical and UV fluxes indicates the UV light is not dominated by any hot population but rather represents the general UV characteristics of the underlying stellar population. In particular, we can place an upper limit of 25 03-5 stars that are present due to possible low level star formation. Furthermore, the UV-optical colors of the dFs are significantly redder than Galactic globular clusters which indicates that these dFs do not have a significant population of extreme horizontal branch stars. With the failure of the near-UV camera aboard the Astro-2 mission, the opportunity for performing a deeper near-UV survey has been lost. We conclude, however, that such a survey would have good sensitivity to the detection of optically faint and/or diffuse galaxies and would provide credible information on the galaxy luminosity function.

The dependence of H II region properties on global and local surface brightness within galaxy discs

Using B, R and Hα images of roughly equal-sized samples of low surface brightness (LSB) and high ... more Using B, R and Hα images of roughly equal-sized samples of low surface brightness (LSB) and high surface brightness (HSB) galaxies (∼40 galaxies apiece), we have explored the dependence of H II region properties on local and global disc surface brightness. We have done this by constructing co-added H II region luminosity functions (LFs) according to local and central disc surface brightness and fitting Schechter functions to these LFs. The results show that the shape of the H II region LF within LSB galaxies does not change noticeably as different limiting (i.e. μ > μ lim) local surface brightness values are used. However, the LFs for HSB galaxies have larger values of L * and are less steep at the faint-end than those of LSB galaxies for limiting B-band local surface brightness values as faint as μ B,lim 23– 24. Both the LFs and the data for individual H II regions show that luminous (L > 10 39 erg s −1) H II regions are much more common within HSB discs than within LSB discs, implying that the newly formed star clusters are also larger. Taking this into account along with the results of Monte Carlo simulations, the shapes of the LFs imply that the regions within LSB discs and those within the LSB areas of HSB discs are relatively old (∼5 Myr) while the regions within HSB discs for μ B 24 are significantly younger (<1 Myr). Since the majority of the LSB galaxies do not have noticeable spiral arms and the majority of the HSB galaxies do, this may indicate a transition within HSB discs from spiral arm-driven star formation to a more locally driven, possibly sporadic form of star formation at μ B ∼ 24, a transition that does not appear to occur within LSB discs.

STELLAR POPULATIONS IN SHELL GALAXIES

UBV surface photometry of the shell galaxies Arp 230, NGC 7010, and Arp 223 is presented. We find... more UBV surface photometry of the shell galaxies Arp 230, NGC 7010, and Arp 223 is presented. We find all to be the result of mergers. In Arp 230, the merger of two spirals induced a burst of star formation which has declined in strength since the collision. The remnant seems likely to become elliptical. NGC 7010 has very red shells, perhaps redder than the galaxy itself. Evolution of the stellar content of these shells may be important. Arp 223 has shell colors which are slightly bluer than the main body of the galaxy, consistent with an origin in an Sb. Our data indicate that the timescale since the interaction is typically ^ 1 Gyr. Moreover, those ellipticals that have been formed by mergers should have complex stellar populations with a component formed in the collision. This extra component might be detectable by the methods of empirical population synthesis, at least to some age limit, making it possible to investigate the relative numbers of ellipticals formed in this manner by methods other than morphology.

THE EFFECTS OF STARBURST ACTIVITY ON LOW SURFACE BRIGHTNESS DISK GALAXIES

Although numerous simulations have been done to understand the e †ects of intense bursts of star ... more Although numerous simulations have been done to understand the e †ects of intense bursts of star formation on high surface brightness galaxies, few attempts have been made to understand how localized starbursts would a †ect both the color and surface brightness of low surface brightness (LSB) galaxies. To remedy this, we have run 53 simulations involving bursts of star formation activity on LSB galaxies, varying both the underlying galaxy properties and the parameters describing the starbursts. We discovered that although changing the total color of a galaxy was fairly straightforward, it was virtually impossible to alter a galaxyÏs central surface brightness and thereby remove it from the LSB galaxy clas-siÐcation without placing a high (and fairly artiÐcial) threshold for the underlying gas density. The primary e †ect of large amounts of induced star formation was to produce a centralized core (bulge) component , which is generally not observed in LSB galaxies. The noisy morphological appearance of LSB galaxies, as well as their noisy surface brightness proÐles, can be reproduced by considering small bursts of star formation that are localized within the disk. The trigger mechanism for such bursts is likely distant/weak tidal encounters. The stability of disk central surface brightness to these periods of star formation argues that the large space density of LSB galaxies at z \ 0 should hold to substantially higher redshifts.

STAR FORMATION IN GALAXIES WITH LARGE LOWER SURFACE BRIGHTNESS DISKS

We present B, R, and H imaging data of 19 large disk galaxies whose properties are intermediate b... more We present B, R, and H imaging data of 19 large disk galaxies whose properties are intermediate between classical low surface brightness galaxies and ordinary high surface brightness galaxies. We use data taken from the Lowell 1.8 m Perkins telescope to determine the galaxies' overall morphology, color, and star formation properties. Morphologically, the galaxies range from Sb through Irr and include galaxies with and without nuclear bars. The colors of the galaxies vary from B À R ¼ 0:3 to 1.9, and most show at least a slight bluing of the colors with increasing radius. The H images of these galaxies show an average star formation rate lower than is found for similar samples with higher surface brightness disks. In addition, the galaxies studied have both higher gas mass-to-luminosity ratios and more diffuse H emission than is found in higher surface brightness samples.

THE SPATIAL EXTENT OF (U)LIRGs IN THE MID-INFRARED. I. THE CONTINUUM EMISSION

We present an analysis of the extended mid-infrared (MIR) emission of the Great Observatories All... more We present an analysis of the extended mid-infrared (MIR) emission of the Great Observatories All-Sky LIRG Survey sample based on 5–15 μm low-resolution spectra obtained with the Infrared Spectrograph on Spitzer. We calculate the fraction of extended emission (FEE) as a function of wavelength for the galaxies in the sample, FEE λ , defined as the fraction of the emission which originates outside of the unresolved component of a source at a given distance. We find that the FEE λ varies from one galaxy to another, but we can identify three general types of FEE λ : one where FEE λ is constant, one where features due to emission lines and polycyclic aromatic hydrocarbons appear more extended than the continuum, and a third which is characteristic of sources with deep silicate absorption at 9.7 μm. More than 30% of the galaxies have a median FEE λ larger than 0.5, implying that at least half of their MIR emission is extended. Luminous Infrared Galaxies (LIRGs) display a wide range of FEE in their warm dust continuum (0 FEE 13.2 μm 0.85). The large values of FEE 13.2 μm that we find in many LIRGs suggest that the extended component of their MIR continuum emission originates in scales up to 10 kpc and may contribute as much as the nuclear region to their total MIR luminosity. The mean size of the LIRG cores at 13.2 μm is 2.6 kpc. However, once the IR luminosity of the systems reaches the threshold of L IR ∼ 10 11.8 L , slightly below the regime of Ultra-luminous Infrared Galaxies (ULIRGs), all sources become clearly more compact, with FEE 13.2 μm 0.2, and their cores are unresolved. Our estimated upper limit for the core size of ULIRGs is less than 1.5 kpc. Furthermore, our analysis indicates that the compactness of systems with L IR 10 11.25 L strongly increases in those classified as mergers in their final stage of interaction. The FEE 13.2 μm is also related to the contribution of an active galactic nucleus (AGN) to the MIR emission. Galaxies which are more AGN dominated are less extended, independently of their L IR. We finally find that the extent of the MIR continuum emission is correlated with the far-IR IRAS log(f 60 μm /f 100 μm) color. This enables us to place a lower limit to the area in a galaxy from where the cold dust emission may originate, a prediction which can be tested soon with the Herschel Space Telescope.

MID-INFRARED PROPERTIES OF NEARBY LUMINOUS INFRARED GALAXIES. I. SPITZER INFRARED SPECTROGRAPH SPECTRA FOR THE GOALS SAMPLE

The Great Observatories All-Sky LIRG Survey (GOALS) is a comprehensive, multiwavelength study of ... more The Great Observatories All-Sky LIRG Survey (GOALS) is a comprehensive, multiwavelength study of luminous infrared galaxies (LIRGs) in the local universe. Here we present low resolution Spitzer Infrared Spectrograph spectra covering 5–38 μm and provide a basic analysis of the mid-IR spectral properties observed for nearby LIRGs. In a companion paper, we discuss detailed fits to the spectra and compare the LIRGs to other classes of galaxies. The GOALS sample of 244 nuclei in 180 luminous (10 11 L IR /L < 10 12) and 22 ultraluminous (L IR /L 10 12) IR galaxies represents a complete subset of the IRAS Revised Bright Galaxy Sample and covers a range of merger stages, morphologies, and spectral types. The majority (>60%) of the GOALS LIRGs have high 6.2 μm polycyclic aromatic hydrocarbon (PAH) equivalent widths (EQW 6.2 μm > 0.4 μm) and low levels of silicate absorption (s 9.7 μm > −1.0). There is a general trend among the U/LIRGs for both silicate depth and mid-infrared (MIR) slope to increase with increasing L IR. U/LIRGs in the late to final stages of a merger also have, on average, steeper MIR slopes and higher levels of dust obscuration. Together, these trends suggest that as gas and dust is funneled toward the center of a coalescing merger, the nuclei become more compact and more obscured. As a result, the dust temperature increases also leading to a steeper MIR slope. The sources that depart from these correlations have very low PAH equivalent width (EQW 6.2 μm < 0.1 μm) consistent with their emission being dominated by an active galactic nucleus (AGN) in the MIR. These extremely low PAH EQW sources separate into two distinct types: relatively unobscured sources with a very hot dust component (and thus very shallow MIR slopes) and heavily dust obscured nuclei with a steep temperature gradient. The most heavily dust obscured sources are also the most compact in their MIR emission, suggesting that the obscuring (cool) dust is associated with the outer regions of the starburst and not simply a measure of the dust along the line of sight through a large, dusty disk. A marked decline is seen for the fraction of high EQW (star formation dominated) sources as the merger progresses. The decline is accompanied by an increase in the fraction of composite sources while the fraction of sources where an AGN dominates the MIR emission remains low. When compared to the MIR spectra of submillimeter galaxies (SMGs) at z ∼ 2, both the average GOALS LIRG and ULIRG spectra are more absorbed at 9.7 μm and the average GOALS LIRG has more PAH emission. However, when the AGN contributions to both the local GOALS LIRGs and the high-z SMGs are removed, the average local starbursting LIRG closely resembles the starburst-dominated SMGs.

Stellar populations in shell galaxies

Astron J, 1990

UBV surface photometry of the shell galaxies Arp 230, NGC 7010, and Arp 223 is presented and all ... more UBV surface photometry of the shell galaxies Arp 230, NGC 7010, and Arp 223 is presented and all are found to be the result of mergers. In Arp 230. the merger of two spirals induced a burst of star formation which has declined in strength since the collision. The remnant seems likely to become elliptical. NGC 7010 has very red shells, perhaps redder than the galaxy itself. Evolution of the stellar content of these shells may be important. Arp 223 has shell colors which are slightly bluer than the main body of the galaxy, consistent with an origin in an Sb. Data indicate that the timescale since the interaction is typically approximately equal to 1 Gyr. Moreover, those ellipticals that have been formed by mergers should have complex stellar populations with a component formed in the collision. This extra component might be detectable by the methods of empirical population synthesis, at least to some age limit, making it possible to investigate the relative numbers of ellipticals formed in this manner by methods other than morphology.

Far‐Ultraviolet and Hα Imaging of Nearby Spiral Galaxies: The OB Stellar Population in the Diffuse Ionized Gas

The Astrophysical Journal, 2001

We have compared Hα and far ultraviolet (FUV) images of 10 nearby spirals, with the goal of under... more We have compared Hα and far ultraviolet (FUV) images of 10 nearby spirals, with the goal of understanding the contribution of field OB stars to the ionization of the diffuse ionized gas (DIG) in spiral galaxies. The FUV images were obtained by the Ultraviolet Imaging Telescope (UIT) and the Hα images were obtained using various ground-based telescopes. In all of the galaxies, the F Hα /F U IT flux ratio is lower in the DIG than in the H II regions. This is likely an indication that the mean spectral type for OB stars in the field is later than that in H II regions. Comparison of the N Lyc /L U IT ratio with models of evolving stellar populations shows that the stellar population in the DIG is consistent with either an older single burst population or a steady state model with constant star formation and an initial mass function (IMF) slope steeper than α=2.35. The steady state model is probably a more realistic representation of the stellar population outside of H II regions. The steep IMF slope simulates the steep present-day mass function slope expected for field OB stars, and does not necessarily indicate that IMF slope is actually steeper than α=2.35. We compared the F Hα /F U IT ratio in the DIG of these galaxies with that in M33, in which the field OB stellar population has previously been investigated using Hubble Space Telescope images. If the mean spectral types of stars in H II regions and in the DIG are the same as in M33, and the difference in extinction between DIG and H II regions is constant among galaxies, then the analysis suggests that field stars are important sources of ionization in most galaxies, and may be the dominant source in some galaxies.

Ultraviolet Imaging of NGC 3310: A Merger-driven Global Starburst

The Astrophysical Journal, 1996

We present the first far-ultraviolet (FUV; 1 1500 Å) image of the nearby peculiar SAB(r)bc galaxy... more We present the first far-ultraviolet (FUV; 1 1500 Å) image of the nearby peculiar SAB(r)bc galaxy NGC 3310. The small 15Љ (945 pc) diameter circumnuclear starburst ring is the most luminous structure, producing 30% of the total observed FUV luminosity. Diffuse emission from the inner disk (20Љ Ͻ R Ͻ 40Љ) contributes another 120% of the observed FUV flux. A linear feature (the "arrow") appears to be a star-forming tidal feature. A diffuse arc observed at optical wavelengths (the "bow") is not visible in the FUV and is probably a tidally induced shell composed of older stars. Mean star formation rates range from 0.031 M J yr Ϫ1 kpc Ϫ2 in the arrow to 2.1 M J yr Ϫ1 kpc Ϫ2 at the brightest FUV source. The striking similarity between the R 1/4 law behavior of the FUV and B-band surface brightness profiles, combined with the very blue colors of NGC 3310, strongly argues that the present morphology is the result of a global starburst triggered by a merger with a dwarf companion.

Two-color CCD mapping of the luminous Type I irregular galaxy NGC 4449

The Astronomical Journal, 1986

The luminosities of bright H II regions in NGC 628 and its O star formation rate

The Astronomical Journal, 1990

STAR FORMATION IN H i–SELECTED GALAXIES. II. H ii REGION PROPERTIES

by Gregory Bothun and Rene Walterbos

A sample of 69 galaxies with radial velocities less than 2500 km s À1 was selected from the H i P... more A sample of 69 galaxies with radial velocities less than 2500 km s À1 was selected from the H i Parkes All Sky Survey (HiPASS) to deduce details about star formation in nearby disk galaxies selected with no bias to optical surface brightness selection effects. Broadband (B and R) and narrowband (H) images were obtained for all of these objects. More than half of the sample galaxies are late-type, dwarf disks (mostly Sc and Sm galaxies). We have measured the properties of the H ii regions on H continuum–subtracted images, using the HIIphot package developed by Thilker et al. All but one of the galaxies contained at least one detectable H ii region. Examination of the properties of the H ii regions in each galaxy revealed that the brightest regions in higher surface brightness galaxies tend to be more luminous than those in lower surface brightness galaxies. A higher fraction (referred to as the diffuse fraction) of the H emission from lower surface brightness galaxies comes from diffuse ionized gas. H ii region luminosity functions (LFs) co-added according to surface brightness show that the shapes of the LFs for the lowest surface brightness galaxies are different from those for typical spiral galaxies. This discrepancy could be caused by the lowest surface brightness galaxies having somewhat episodic star formation or by them forming a relatively larger fraction of their stars outside of dense, massive molecular clouds. In general, the results imply that the conditions under which star formation occurs in lower surface brightness galaxies are different than in more typical, higher surface brightness spiral galaxies.

STAR FORMATION IN H i–SELECTED GALAXIES. I. SAMPLE CHARACTERISTICS

A sample of 69 galaxies with radial velocities of less than 2500 km s À1 was selected from the H ... more A sample of 69 galaxies with radial velocities of less than 2500 km s À1 was selected from the H i Parkes All-Sky Survey (HIPASS) and imaged in broadband B and R and narrowband H, to deduce details about star formation in nearby disk galaxies while avoiding surface brightness selection effects. The sample is dominated by late-type, dwarf disks (mostly Sc and Sm galaxies) with exponential disk scale lengths of $1–5 kpc. The HIPASS galaxies, on average, have lower star formation rates (SFRs), are bluer, and have lower surface brightness than an optically selected sample. H ii regions were detected in all but one of the galaxies. Many galaxies had as few as two to five H ii regions. The galaxies' H equivalent widths, colors, and SFRs per unit of H i mass are best explained by young mean ages ($3–5 Gyr, according to Schmidt-law models) with star formation histories in which the SFRs were higher in the past. Comparison of the surface brightness coverage of the HIPASS galaxies with that of an optically selected sample shows that such a sample may miss $10% of the local galaxy number density and could possibly miss as much as 3%–4% of the SFR density. The amount lower surface brightness galaxies contribute to the total luminosity density may be insignificant, but this conclusion is somewhat dependent on how the fluxes of these objects are determined.

Surface photometry of disk galaxies at 60 and 100 microns - Radial gradients in dust temperature in optically thin disks

The Astronomical Journal, 1992

Precision Velocity Fields in Spiral Galaxies. II. Rotation Curves

The Astrophysical Journal Supplement Series, 2001

Imaging Fabry-Perot data has been acquired for a sample of seven late-type spiral galaxies from w... more Imaging Fabry-Perot data has been acquired for a sample of seven late-type spiral galaxies from which two-dimensional velocity Ðelds have been constructed on a subkiloparsec resolution scale. The kinematic disk (i.e., tilted ring) modeling procedure is used to Ðt the velocity Ðeld and recover its rotational structure. From this Ðt, di †erent schemes are used to extract the major-axis rotation curve, as well as velocity proÐles along the minor axis. Rotation curves found from deprojection of the velocity Ðeld using mean geometric parameters invariably produce small-scale "" bumps and wiggles,ÏÏ which are a reÑection of the inclusion of noncircular motions. In the bestÈrotation curve method, the rotation curve is derived from the best Ðt to the entire velocity Ðeld. This method is shown to minimize the e †ects of noncircular motions. The kinematic center of the velocity Ðeld is allowed to vary, and those results are directly compared with cases where the kinematic center is held Ðxed. In virtually all cases, we Ðnd that the variable center model produces the smoothest and most symmetric rotation curves and minor-axis velocity proÐles. Our results indicate that the kinematic center of mass is moving around in these disk systems with an amplitude of plus or minus D300 pc. Finally, we investigate the e †ects of small, systematic errors in centering and Ðnd that small minor-axis displacements can artiÐcially produce spurious slopes in the rotation curve at large radius, including producing rotation curves that are apparently falling.

Precision Velocity Fields in Spiral Galaxies. I. Noncircular Motions and rms Noise in Disks

Astrophys J Suppl Ser, 2000

Investigation of the symmetry of the major-and minor-axis rotation curves reveals strong evidence... more Investigation of the symmetry of the major-and minor-axis rotation curves reveals strong evidence of nonconcentric gas orbits with the maximum center shift of D300 pc. Comparisons between kinematic and photometric structure (e.g., position angles, inclinations, centers) show considerable noise on small scales. Although large-scale averages are in agreement, this noise is a matter of some concern in the application of the Tully-Fisher method to disk galaxies. Moreover, cases of signiÐcant misalignment in position angle between the inner and outer disks are seen in two of the sample galaxies and may indicate the transition between luminous and dark-matterÈdominated regions (i.e., where the maximum-disk hypothesis begins to fail).

Kinematics of star cluster in M33

The Astronomical Journal, 1991

The bulge/halo luminosity of M33 and its globular cluster population

The Astronomical Journal, 1992

A CONSTRAINT ON THE INFALL OF H I INTO BIG DISK GALAXIES

Available 21-cm observations of late-type spirals from a variety of sources have been gathered to... more Available 21-cm observations of late-type spirals from a variety of sources have been gathered together for purposes of constructing an H i luminosity function for spirals with M B < — 18. Over the range 9.0<log Af H < 10.0 this luminosity function is well represented by a power law with slope near unity, but with an abrupt cutoff at log Af H = 10.2. This truncation suggests that most high-luminosity spirals are not surrounded by halos that contain relatively large amounts of H I. To fortify this suggestion, we have observed a sample of 59 late-type, intrinsically large sprial galaxies whose disk H i masses are constant to within 40%. Observing this standard H i candle over a large range in redshift (5000-18 000 km s-1) has enabled increasingly larger volumes of space that surround the disk to become accessible to the Arecibo 21-cm beam. The data show absolutely no trend of increasing H i with redshift. There is likewise no tendency for an increase in observed H I mass over that predicted from the linear diameter of the galaxy, as the ratio of beam size to galaxy size increases. From these null results we can place an upper limit on the halo H i column density of A H = 3x 10 19 atoms cm-2. In relative terms, the halo can contain no more than 1/3 the amount of H i already distributed in the disk. Based on these data, we argue that, if infall is still important at the present time in the evolution of big disk galaxies, then the reservoir should be detectable unless it is predominately in a form more exotic than atomic hydrogen.

Near-IR Surface Photometry of Galaxies: Expectations, Techniques and Real Data

Beyond the Hubble Sequence