We compare the molecular and ionized gas velocity dispersions of nine nearby turbulent disks, ana... more We compare the molecular and ionized gas velocity dispersions of nine nearby turbulent disks, analogs to high-redshift galaxies, from the DYNAMO sample using new Atacama Large Millimeter/submillimeter Array and GMOS/Gemini observations. We combine our sample with 12 galaxies at z ∼ 0.5–2.5 from the literature. We find that the resolved velocity dispersion is systematically lower by a factor 2.45 ± 0.38 for the molecular gas compared to the ionized gas, after correcting for thermal broadening. This offset is constant within the galaxy disks and indicates the coexistence of a thin molecular gas disk and a thick ionized one. This result has a direct impact on the Toomre Q and pressure derived in galaxies. We obtain pressures ∼0.22 dex lower on average when using the molecular gas velocity dispersion, σ 0,mol. We find that σ 0,mol increases with gas fraction and star formation rate. We also obtain an increase with redshift and show that the EAGLE and FIRE simulations overall overestimat...
Monthly Notices of the Royal Astronomical Society, 2017
We present Keck/OSIRIS adaptive optics observations with 150-400 pc spatial sampling of 7 turbule... more We present Keck/OSIRIS adaptive optics observations with 150-400 pc spatial sampling of 7 turbulent, clumpy disc galaxies from the DYNAMO sample (0.07 < z < 0.2). DYNAMO galaxies have previously been shown to be well matched in properties to main sequence galaxies at z ∼ 1.5. Integral field spectroscopy observations using adaptive optics are subject to a number of systematics including a variable PSF and spatial sampling, which we account for in our analysis. We present gas velocity dispersion maps corrected for these effects, and confirm that DYNAMO galaxies do have high gas velocity dispersion (σ = 40 − 80 km s −1), even at high spatial sampling. We find statistically significant structure in 6 out of 7 galaxies. The most common distance between the peaks in velocity dispersion (σ peaks) and emission line peaks is ∼ 0.5 kpc, we note this is very similar to the average size of a clump measured with HST Hα maps. This could suggest that σ peaks in clumpy galaxies likely arise due to some interaction between the clump and the surrounding ISM of the galaxy, though our observations cannot distinguish between outflows, inflows or velocity shear. Observations covering a wider area of the galaxies will be needed to confirm this result.
We measure the stellar specific angular momentum j s = J s /M s in four nearby (z ≈ 0.1) disk gal... more We measure the stellar specific angular momentum j s = J s /M s in four nearby (z ≈ 0.1) disk galaxies that have stellar masses M s near the break M * s of the galaxy mass function, but look like typical starforming disks at z ≈ 2 in terms of their low stability (Q ≈ 1), clumpiness, high ionized gas dispersion (40−50 km s −1), high molecular gas fraction (20−30%) and rapid star formation (∼ 20 M yr −1). Combining high-resolution (Keck-OSIRIS) and large-radius (Gemini-GMOS) spectroscopic maps, only available at low z, we discover that these targets have ∼ 3 times less stellar angular momentum than typical local spiral galaxies of equal stellar mass and bulge fraction. Theoretical considerations show that this deficiency in angular momentum is the main cause of their low stability, while the high gas fraction plays a complementary role. Interestingly, the low j s values of our targets are similar to those expected in the M * s-population at higher z from the approximate theoretical scaling j s ∝ (1 + z) −1/2 at fixed M s. This suggests that a change in angular momentum, driven by cosmic expansion, is the main cause for the remarkable difference between clumpy M * s-disks at high z (which likely evolve into early-type galaxies) and mass-matched local spirals.
We present an inventory of galaxy bulge types (elliptical galaxy, classical bulge, pseudobulge, a... more We present an inventory of galaxy bulge types (elliptical galaxy, classical bulge, pseudobulge, and bulgeless galaxy) in a volume-limited sample within the local 11 Mpc sphere using Spitzer 3.6 μm and Hubble Space Telescope data. We find that whether counting by number, star formation rate, or stellar mass, the dominant galaxy type in the local universe has pure disk characteristics (either hosting a pseudobulge or being bulgeless). Galaxies that contain either a pseudobulge or no bulge combine to account for over 80% of the number of galaxies above a stellar mass of 10 9 M. Classical bulges and elliptical galaxies account for ∼1/4, and disks for ∼3/4 of the stellar mass in the local 11 Mpc. About 2/3 of all star formation in the local volume takes place in galaxies with pseudobulges. Looking at the fraction of galaxies with different bulge types as a function of stellar mass, we find that the frequency of classical bulges strongly increases with stellar mass, and comes to dominate above 10 10.5 M. Galaxies with pseudobulges dominate at 10 9.5-10 10.5 M. Yet lower-mass galaxies are most likely to be bulgeless. If pseudobulges are not a product of mergers, then the frequency of pseudobulges in the local universe poses a challenge for galaxy evolution models.
We investigate the correlation between CO and H I emission in 18 nearby galaxies from the CARMA S... more We investigate the correlation between CO and H I emission in 18 nearby galaxies from the CARMA Survey Toward IR-Bright Nearby Galaxies (STING) at sub-kpc and kpc scales. Our sample, spanning a wide range in stellar mass and metallicity, reveals evidence for a metallicity dependence of the H I column density measured in regions exhibiting CO emission. Such a dependence is predicted by the equilibrium model of McKee & Krumholz, which balances H 2 formation and dissociation. The observed H I column density is often smaller than predicted by the model, an effect we attribute to unresolved clumping, although values close to the model prediction are also seen. We do not observe H I column densities much larger than predicted, as might be expected were there a diffuse H I component that did not contribute to H 2 shielding. We also find that the H 2 column density inferred from CO correlates strongly with the stellar surface density, suggesting that the local supply of molecular gas is tightly regulated by the stellar disk.
New surface photometry of all known elliptical galaxies in the Virgo cluster is combined with pub... more New surface photometry of all known elliptical galaxies in the Virgo cluster is combined with published data to derive composite profiles of brightness, ellipticity, position angle, isophote shape, and color over large radius ranges. These provide enough leverage to show that Sérsic log I ∝ r 1/n functions fit the brightness profiles I(r) of nearly all ellipticals remarkably well over large dynamic ranges. Therefore we can confidently identify departures from these profiles that are diagnostic of galaxy formation. Two kinds of departures are seen at small radii. All 10 of our ellipticals with total absolute magnitudes M V T ≤ −21.66 have cuspy cores-"missing light"-at small radii. Cores are well known and naturally scoured by binary black holes formed in dissipationless ("dry") mergers. All 17 ellipticals with −21.54 ≤ M V T ≤ −15.53 do not have cores. We find a new distinct component in these galaxies: All coreless ellipticals in our sample have extra light at the center above the inward extrapolation of the outer Sérsic profile. In large ellipticals, the excess light is spatially resolved and resembles the the central components predicted in numerical simulations of mergers of galaxies that contain gas. In the simulations, the gas dissipates, falls toward the center, undergoes a starburst, and builds a compact stellar component that, as in our observations, is distinct from the Sérsic-function main body of the elliptical. But ellipticals with extra light also contain supermassive black holes. We suggest that the starburst has swamped core scouring by binary black holes. That is, we interpret extra light components as a signature of formation in dissipative ("wet") mergers. Besides extra light, we find three new aspects to the ("E-E") dichotomy into two types of elliptical galaxies. Core galaxies are known to be slowly rotating, to have relatively anisotropic velocity distributions, and to have boxy isophotes. We show that they have Sérsic indices n > 4 uncorrelated with M V T. They also are α-element enhanced, implying short star formation timescales. And their stellar populations have a variety of ages but mostly are very old. Extra light ellipticals generally rotate rapidly, are more isotropic than core Es, and have disky isophotes. We show that they have n ≃ 3 ± 1 almost uncorrelated with M V T and younger and less α-enhanced stellar populations. These are new clues to galaxy formation. We suggest that extra light ellipticals got their low Sérsic indices by forming in relatively few binary mergers, whereas giant ellipticals have n > 4 because they formed in larger numbers of mergers of more galaxies at once plus later heating during hierarchical clustering. We confirm that core Es contain X-ray-emitting gas whereas extra light Es generally do not. This leads us to suggest why the E-E dichotomy arose. If AGN energy feedback requires a "working surface" of hot gas, then this is present in core galaxies but absent in extra light galaxies. We suggest that AGN energy feedback is a strong function of galaxy mass: it is weak enough in small Es not to prevent merger starbursts, but strong enough in giant Es and their progenitors to make dry mergers dry and to protect old stellar populations from late star formation. Finally, we verify that there is a strong dichotomy between elliptical and spheroidal galaxies. Their properties are consistent with our understanding of their different formation processes: mergers for ellipticals and conversion of late-type galaxies into spheroidals by environmental effects and by energy feedback from supernovae. In an Appendix, we develop machinery to get realistic error estimates for Sérsic parameters even when they are strongly coupled. And we discuss photometric dynamic ranges necessary to get robust results from Sérsic fits.
We investigate scaling relations of bulges using bulge-disk decompositions at 3.6 μm and present ... more We investigate scaling relations of bulges using bulge-disk decompositions at 3.6 μm and present bulge classifications for 173 E-Sd galaxies within 20 Mpc. Pseudobulges and classical bulges are identified using Sérsic index, Hubble Space Telescope morphology, and star formation activity (traced by 8 μm emission). In the near-IR pseudobulges have n b < 2 and classical bulges have n b > 2, as found in the optical. Sérsic index and morphology are essentially equivalent properties for bulge classification purposes. We confirm, using a much more robust sample, that the Sérsic index of pseudobulges is uncorrelated with other bulge structural properties, unlike for classical bulges and elliptical galaxies. Also, the half-light radius of pseudobulges is not correlated with any other bulge property. We also find a new correlation between surface brightness and pseudobulge luminosity; pseudobulges become more luminous as they become more dense. Classical bulges follow the well-known scaling relations between surface brightness, luminosity, and half-light radius that are established by elliptical galaxies. We show that those pseudobulges (as indicated by Sérsic index and nuclear morphology) that have low specific star formation rates are very similar to models of galaxies in which both a pseudobulge and classical bulge exist. Therefore, pseudobulge identification that relies only on structural indicators is incomplete. Our results, especially those on scaling relations, imply that pseudobulges are very different types of objects than elliptical galaxies.
Monthly Notices of the Royal Astronomical Society, 2021
We present detailed stellar specific angular momentum (j*) measurements of 10 star-forming galaxi... more We present detailed stellar specific angular momentum (j*) measurements of 10 star-forming galaxies at z ∼ 1.5−2, using both high and low spatial resolution integral field spectroscopic data. We developed a code that simultaneously models the adaptive optics (AO) assisted observations from OSIRIS/SINFONI along with their natural seeing (NS) counterparts from KMOS at spatial resolutions of [0.1−0.4] arcsec and [0.6−1.0] arcsec, respectively. The AO data reveal 2/10 systems to be mergers and for the remaining eight the mean uncertainties $\bar{\Delta }j_*$ decrease from 49 per cent (NS), and 26.5 per cent (AO), to 16 per cent in the combined analysis. These j* measurements agree within 20 per cent with simple estimates ($\tilde{j_*}$) calculated from Hubble Space Telescope photometry and NS kinematics; however, higher resolution kinematics are required to first identify these discs. We find that the choice of surface mass density model and the measurement of effective radius from phot...
In this paper, we study the properties of pseudobulges (bulges that appear similar to disk galaxi... more In this paper, we study the properties of pseudobulges (bulges that appear similar to disk galaxies) and classical bulges (bulges which appear similar to E-type galaxies) in bulge-disk decompositions. We show that the distribution of bulge Sérsic indices, n b , is bimodal, and this bimodality correlates with the morphology of the bulge. Pseudobulges have n b 2 and classical bulges have n b 2 with little to no overlap. Also, pseudobulges do not follow the correlations of Sérsic index with structural parameters or the photometric projections of the fundamental plane in the same way that classical bulges and elliptical galaxies do. We find that pseudobulges are systematically flatter than classical bulges and thus more disk-like in both their morphology and shape. We do not find significant differences between different bulge morphologies which we are collectively calling pseudobulges (nuclear spirals, nuclear rings, nuclear bars, and nuclear patchiness); they appear to behave similarly in all parameter correlations. In the Sérsic index, flattening, and bulge-to-total ratio, the distinction appears to be between classical bulges and pseudobulges, not between different pseudobulge morphologies. The Sérsic index of the pseudobulges does not correlate with B/T , in contrast to classical bulges. Also, the half-light radius of the pseudobulge correlates with the scale length of the disk; this is not the case for classical bulges. The correlation of Sérsic index and scale lengths with bulge morphology suggests that secular evolution is creating pseudobulges with low-Sérsic index and that other processes (e.g., major mergers) are responsible for the higher Sérsic index in classical bulges and elliptical galaxies.
The objective of the Phoenix mission is to determine if Mars' polar region can support life. ... more The objective of the Phoenix mission is to determine if Mars' polar region can support life. Since liquid water is a basic ingredient for life, as we know it, an important goal of the mission is to determine if liquid water exists at the landing site. It is believed that a layer of Martian soil preserves ice by forming a barrier against high temperatures and sublimation, but that exposed ice sublimates without the formation of the liquid phase. Here we show possible independent physical and thermodynamical evidence that besides ice, liquid saline water exists in areas disturbed by the Phoenix Lander. Moreover, we show that the thermodynamics of freeze‐thaw cycles can lead to the formation of saline solutions with freezing temperatures lower than current summer ground temperatures on the Phoenix landing site on Mars' Arctic. Thus, we hypothesize that liquid saline water might occur where ground ice exists near the Martian surface. The ideas and results presented in this artic...
The northern Afar depression of eastern Ethiopia constitutes a young and active rift of the Earth... more The northern Afar depression of eastern Ethiopia constitutes a young and active rift of the Earth's crust, with characters similar to those of oceanic rifts; it can be considered a continuation of the Red Sea rift. We report here on the geochemistry of a Fe-Mn-Ba deposit formed about 200,000 years ago when the Afar Rift was submerged as a branch of the Red Sea. The deposit is associated with fossil coral reefs and is underlain by a submarine basaltic formation. The deposit consists of Fe-rich basal layers with goethite and nontronite as principal constituents overlain by Mn-rich strata which at some levels approach a pure pyrolusite ore. Some of the Mn-rich layers are characterized by high contents of Ba (up to about 6 percent) in the form of crystals of strontiobarite containing up to 12 percent SrSO4 in solid solution. The concentration of Ni, Co, Cr and Cu both in the Fe-rich and Mn-rich layers is very low when compared with marine sedimentary Fe-Mn deposits. The U and Th isotopic chemistry of samples from the deposit indicate that the Fe and Mn minerals were not deposited from normal sea water. The data suggest that the deposit was formed as a result of submarine hydrothermal activity whereby solutions rich in Fe, Mn, Ba, Si and other elements were injected through the sea floor and fractional precipitation of these elements followed. The Afar deposits have strong similarities to the hot brine metalliferous deposits from the Red Sea and to deposits from active oceanic rifts, especially the East Pacific Rise.
The Laurentide Ice Sheet (LIS) occupied a large part of North-America during the late Pleistocene... more The Laurentide Ice Sheet (LIS) occupied a large part of North-America during the late Pleistocene. Determining the proper surface geometry and elevation of the LIS is of central importance to estimate global changes in sea-level and atmospheric circulation patterns during the late Pleistocene and Holocene. Despite largely disappearing from the landscape during the late Holocene, LIS remnants are found in the Penny and Barnes ice caps on Baffin Island (Canada) and ongoing permafrost degradation has been exposing relics of the LIS buried along its northern margin since the late Pleistocene. Here, we use the δO records of six LIS remnants and the late Pleistocene δO-elevation relation to establish ice elevation in their source area during the last glacial maximum (LGM). Contrary to some modeled reconstructions, our findings indicate an asymmetric LIS topography with higher ice on Keewatin Dome (~3200 m) and thinner ice in the prairies along the Plains divide (1700-2100 m) during LGM. T...
Proceedings of the National Academy of Sciences of the United States of America, Jun 16, 2017
We present a revised and extended high Arctic air temperature reconstruction from a single proxy ... more We present a revised and extended high Arctic air temperature reconstruction from a single proxy that spans the past ∼12,000 y (up to 2009 CE). Our reconstruction from the Agassiz ice cap (Ellesmere Island, Canada) indicates an earlier and warmer Holocene thermal maximum with early Holocene temperatures that are 4-5 °C warmer compared with a previous reconstruction, and regularly exceed contemporary values for a period of ∼3,000 y. Our results show that air temperatures in this region are now at their warmest in the past 6,800-7,800 y, and that the recent rate of temperature change is unprecedented over the entire Holocene. The warmer early Holocene inferred from the Agassiz ice core leads to an estimated ∼1 km of ice thinning in northwest Greenland during the early Holocene using the Camp Century ice core. Ice modeling results show that this large thinning is consistent with our air temperature reconstruction. The modeling results also demonstrate the broader significance of the en...
Because of snow drifting, two time series of any variable derived from two adjacent ice cores wil... more Because of snow drifting, two time series of any variable derived from two adjacent ice cores will differ considerably. The size and statistical nature of this noise element is discussed for two kinds of measured substance. A theory is developed and compared to data from Greenland and Canadian Arctic ice cores. In case 1, the measured substance can diffuse and the seasonal cycle degrade with time and depth, e.g. δ(18O). In case 2, the measured substance cannot diffuse, e.g. microparticles. The case 2 time series contain drift noise proportional to that in the accumulation series. For accumulation series, the spectral power is concentrated at the high frequencies, i.e. is “blue”. Such noise can be easily reduced by taking relatively short time averages. The noise in the case 1 time series, however, starts out “blue” but quickly diffuses to have a “red” character with significant power at longer wavelengths, and many decades of such series must be averaged to reduce the noise level. B...
■ COMPARISON WITH EMISSION ESTIMATES INSTEAD OF MODEL OUTPUTS Zhang and Kang focus on our suggest... more ■ COMPARISON WITH EMISSION ESTIMATES INSTEAD OF MODEL OUTPUTS Zhang and Kang focus on our suggestion that current estimates of Hg emissions from Colonial and Gold Rush mining are erroneously high. 1 They propose that comparison of the Mount Logan Hg T flux record to modeled atmospheric Hg concentrations or atmospheric deposition, as shown in Figure 1 of their comment, would be more appropriate than our comparison to emission estimates. The global Hg model they highlight uses the same emission estimates to force a 7-reservoir box model, with exchanges between reservoirs governed by first-order rate constants that are constrained by limited modern-day observations. 2 We chose to compare the Mount Logan Hg T record with the emission estimates to avoid further uncertainty associated with the model. We note that the Mount Logan Hg T record returns to background-level fluxes immediately following the Gold Rush, which is inconsistent with both the global Hg model and the assertion by Zhang and Kang that atmospheric Hg levels are cumulative over half a century. Even if the Mount Logan Hg T record is compared with the global Hg model outputs, our suggestion of erroneously high anthropogenic Hg emission estimates from Colonial and Gold Rush mining remains, as shown in Figure 1 of Zhang and Kang. This suggestion is also made in a recent compilation of 22 lake sediment Hg records from around the world 3 and in chemical modeling of the Colonial silver ore mining process. 4
We compare the molecular and ionized gas velocity dispersions of nine nearby turbulent disks, ana... more We compare the molecular and ionized gas velocity dispersions of nine nearby turbulent disks, analogs to high-redshift galaxies, from the DYNAMO sample using new Atacama Large Millimeter/submillimeter Array and GMOS/Gemini observations. We combine our sample with 12 galaxies at z ∼ 0.5–2.5 from the literature. We find that the resolved velocity dispersion is systematically lower by a factor 2.45 ± 0.38 for the molecular gas compared to the ionized gas, after correcting for thermal broadening. This offset is constant within the galaxy disks and indicates the coexistence of a thin molecular gas disk and a thick ionized one. This result has a direct impact on the Toomre Q and pressure derived in galaxies. We obtain pressures ∼0.22 dex lower on average when using the molecular gas velocity dispersion, σ 0,mol. We find that σ 0,mol increases with gas fraction and star formation rate. We also obtain an increase with redshift and show that the EAGLE and FIRE simulations overall overestimat...
Monthly Notices of the Royal Astronomical Society, 2017
We present Keck/OSIRIS adaptive optics observations with 150-400 pc spatial sampling of 7 turbule... more We present Keck/OSIRIS adaptive optics observations with 150-400 pc spatial sampling of 7 turbulent, clumpy disc galaxies from the DYNAMO sample (0.07 < z < 0.2). DYNAMO galaxies have previously been shown to be well matched in properties to main sequence galaxies at z ∼ 1.5. Integral field spectroscopy observations using adaptive optics are subject to a number of systematics including a variable PSF and spatial sampling, which we account for in our analysis. We present gas velocity dispersion maps corrected for these effects, and confirm that DYNAMO galaxies do have high gas velocity dispersion (σ = 40 − 80 km s −1), even at high spatial sampling. We find statistically significant structure in 6 out of 7 galaxies. The most common distance between the peaks in velocity dispersion (σ peaks) and emission line peaks is ∼ 0.5 kpc, we note this is very similar to the average size of a clump measured with HST Hα maps. This could suggest that σ peaks in clumpy galaxies likely arise due to some interaction between the clump and the surrounding ISM of the galaxy, though our observations cannot distinguish between outflows, inflows or velocity shear. Observations covering a wider area of the galaxies will be needed to confirm this result.
We measure the stellar specific angular momentum j s = J s /M s in four nearby (z ≈ 0.1) disk gal... more We measure the stellar specific angular momentum j s = J s /M s in four nearby (z ≈ 0.1) disk galaxies that have stellar masses M s near the break M * s of the galaxy mass function, but look like typical starforming disks at z ≈ 2 in terms of their low stability (Q ≈ 1), clumpiness, high ionized gas dispersion (40−50 km s −1), high molecular gas fraction (20−30%) and rapid star formation (∼ 20 M yr −1). Combining high-resolution (Keck-OSIRIS) and large-radius (Gemini-GMOS) spectroscopic maps, only available at low z, we discover that these targets have ∼ 3 times less stellar angular momentum than typical local spiral galaxies of equal stellar mass and bulge fraction. Theoretical considerations show that this deficiency in angular momentum is the main cause of their low stability, while the high gas fraction plays a complementary role. Interestingly, the low j s values of our targets are similar to those expected in the M * s-population at higher z from the approximate theoretical scaling j s ∝ (1 + z) −1/2 at fixed M s. This suggests that a change in angular momentum, driven by cosmic expansion, is the main cause for the remarkable difference between clumpy M * s-disks at high z (which likely evolve into early-type galaxies) and mass-matched local spirals.
We present an inventory of galaxy bulge types (elliptical galaxy, classical bulge, pseudobulge, a... more We present an inventory of galaxy bulge types (elliptical galaxy, classical bulge, pseudobulge, and bulgeless galaxy) in a volume-limited sample within the local 11 Mpc sphere using Spitzer 3.6 μm and Hubble Space Telescope data. We find that whether counting by number, star formation rate, or stellar mass, the dominant galaxy type in the local universe has pure disk characteristics (either hosting a pseudobulge or being bulgeless). Galaxies that contain either a pseudobulge or no bulge combine to account for over 80% of the number of galaxies above a stellar mass of 10 9 M. Classical bulges and elliptical galaxies account for ∼1/4, and disks for ∼3/4 of the stellar mass in the local 11 Mpc. About 2/3 of all star formation in the local volume takes place in galaxies with pseudobulges. Looking at the fraction of galaxies with different bulge types as a function of stellar mass, we find that the frequency of classical bulges strongly increases with stellar mass, and comes to dominate above 10 10.5 M. Galaxies with pseudobulges dominate at 10 9.5-10 10.5 M. Yet lower-mass galaxies are most likely to be bulgeless. If pseudobulges are not a product of mergers, then the frequency of pseudobulges in the local universe poses a challenge for galaxy evolution models.
We investigate the correlation between CO and H I emission in 18 nearby galaxies from the CARMA S... more We investigate the correlation between CO and H I emission in 18 nearby galaxies from the CARMA Survey Toward IR-Bright Nearby Galaxies (STING) at sub-kpc and kpc scales. Our sample, spanning a wide range in stellar mass and metallicity, reveals evidence for a metallicity dependence of the H I column density measured in regions exhibiting CO emission. Such a dependence is predicted by the equilibrium model of McKee & Krumholz, which balances H 2 formation and dissociation. The observed H I column density is often smaller than predicted by the model, an effect we attribute to unresolved clumping, although values close to the model prediction are also seen. We do not observe H I column densities much larger than predicted, as might be expected were there a diffuse H I component that did not contribute to H 2 shielding. We also find that the H 2 column density inferred from CO correlates strongly with the stellar surface density, suggesting that the local supply of molecular gas is tightly regulated by the stellar disk.
New surface photometry of all known elliptical galaxies in the Virgo cluster is combined with pub... more New surface photometry of all known elliptical galaxies in the Virgo cluster is combined with published data to derive composite profiles of brightness, ellipticity, position angle, isophote shape, and color over large radius ranges. These provide enough leverage to show that Sérsic log I ∝ r 1/n functions fit the brightness profiles I(r) of nearly all ellipticals remarkably well over large dynamic ranges. Therefore we can confidently identify departures from these profiles that are diagnostic of galaxy formation. Two kinds of departures are seen at small radii. All 10 of our ellipticals with total absolute magnitudes M V T ≤ −21.66 have cuspy cores-"missing light"-at small radii. Cores are well known and naturally scoured by binary black holes formed in dissipationless ("dry") mergers. All 17 ellipticals with −21.54 ≤ M V T ≤ −15.53 do not have cores. We find a new distinct component in these galaxies: All coreless ellipticals in our sample have extra light at the center above the inward extrapolation of the outer Sérsic profile. In large ellipticals, the excess light is spatially resolved and resembles the the central components predicted in numerical simulations of mergers of galaxies that contain gas. In the simulations, the gas dissipates, falls toward the center, undergoes a starburst, and builds a compact stellar component that, as in our observations, is distinct from the Sérsic-function main body of the elliptical. But ellipticals with extra light also contain supermassive black holes. We suggest that the starburst has swamped core scouring by binary black holes. That is, we interpret extra light components as a signature of formation in dissipative ("wet") mergers. Besides extra light, we find three new aspects to the ("E-E") dichotomy into two types of elliptical galaxies. Core galaxies are known to be slowly rotating, to have relatively anisotropic velocity distributions, and to have boxy isophotes. We show that they have Sérsic indices n > 4 uncorrelated with M V T. They also are α-element enhanced, implying short star formation timescales. And their stellar populations have a variety of ages but mostly are very old. Extra light ellipticals generally rotate rapidly, are more isotropic than core Es, and have disky isophotes. We show that they have n ≃ 3 ± 1 almost uncorrelated with M V T and younger and less α-enhanced stellar populations. These are new clues to galaxy formation. We suggest that extra light ellipticals got their low Sérsic indices by forming in relatively few binary mergers, whereas giant ellipticals have n > 4 because they formed in larger numbers of mergers of more galaxies at once plus later heating during hierarchical clustering. We confirm that core Es contain X-ray-emitting gas whereas extra light Es generally do not. This leads us to suggest why the E-E dichotomy arose. If AGN energy feedback requires a "working surface" of hot gas, then this is present in core galaxies but absent in extra light galaxies. We suggest that AGN energy feedback is a strong function of galaxy mass: it is weak enough in small Es not to prevent merger starbursts, but strong enough in giant Es and their progenitors to make dry mergers dry and to protect old stellar populations from late star formation. Finally, we verify that there is a strong dichotomy between elliptical and spheroidal galaxies. Their properties are consistent with our understanding of their different formation processes: mergers for ellipticals and conversion of late-type galaxies into spheroidals by environmental effects and by energy feedback from supernovae. In an Appendix, we develop machinery to get realistic error estimates for Sérsic parameters even when they are strongly coupled. And we discuss photometric dynamic ranges necessary to get robust results from Sérsic fits.
We investigate scaling relations of bulges using bulge-disk decompositions at 3.6 μm and present ... more We investigate scaling relations of bulges using bulge-disk decompositions at 3.6 μm and present bulge classifications for 173 E-Sd galaxies within 20 Mpc. Pseudobulges and classical bulges are identified using Sérsic index, Hubble Space Telescope morphology, and star formation activity (traced by 8 μm emission). In the near-IR pseudobulges have n b < 2 and classical bulges have n b > 2, as found in the optical. Sérsic index and morphology are essentially equivalent properties for bulge classification purposes. We confirm, using a much more robust sample, that the Sérsic index of pseudobulges is uncorrelated with other bulge structural properties, unlike for classical bulges and elliptical galaxies. Also, the half-light radius of pseudobulges is not correlated with any other bulge property. We also find a new correlation between surface brightness and pseudobulge luminosity; pseudobulges become more luminous as they become more dense. Classical bulges follow the well-known scaling relations between surface brightness, luminosity, and half-light radius that are established by elliptical galaxies. We show that those pseudobulges (as indicated by Sérsic index and nuclear morphology) that have low specific star formation rates are very similar to models of galaxies in which both a pseudobulge and classical bulge exist. Therefore, pseudobulge identification that relies only on structural indicators is incomplete. Our results, especially those on scaling relations, imply that pseudobulges are very different types of objects than elliptical galaxies.
Monthly Notices of the Royal Astronomical Society, 2021
We present detailed stellar specific angular momentum (j*) measurements of 10 star-forming galaxi... more We present detailed stellar specific angular momentum (j*) measurements of 10 star-forming galaxies at z ∼ 1.5−2, using both high and low spatial resolution integral field spectroscopic data. We developed a code that simultaneously models the adaptive optics (AO) assisted observations from OSIRIS/SINFONI along with their natural seeing (NS) counterparts from KMOS at spatial resolutions of [0.1−0.4] arcsec and [0.6−1.0] arcsec, respectively. The AO data reveal 2/10 systems to be mergers and for the remaining eight the mean uncertainties $\bar{\Delta }j_*$ decrease from 49 per cent (NS), and 26.5 per cent (AO), to 16 per cent in the combined analysis. These j* measurements agree within 20 per cent with simple estimates ($\tilde{j_*}$) calculated from Hubble Space Telescope photometry and NS kinematics; however, higher resolution kinematics are required to first identify these discs. We find that the choice of surface mass density model and the measurement of effective radius from phot...
In this paper, we study the properties of pseudobulges (bulges that appear similar to disk galaxi... more In this paper, we study the properties of pseudobulges (bulges that appear similar to disk galaxies) and classical bulges (bulges which appear similar to E-type galaxies) in bulge-disk decompositions. We show that the distribution of bulge Sérsic indices, n b , is bimodal, and this bimodality correlates with the morphology of the bulge. Pseudobulges have n b 2 and classical bulges have n b 2 with little to no overlap. Also, pseudobulges do not follow the correlations of Sérsic index with structural parameters or the photometric projections of the fundamental plane in the same way that classical bulges and elliptical galaxies do. We find that pseudobulges are systematically flatter than classical bulges and thus more disk-like in both their morphology and shape. We do not find significant differences between different bulge morphologies which we are collectively calling pseudobulges (nuclear spirals, nuclear rings, nuclear bars, and nuclear patchiness); they appear to behave similarly in all parameter correlations. In the Sérsic index, flattening, and bulge-to-total ratio, the distinction appears to be between classical bulges and pseudobulges, not between different pseudobulge morphologies. The Sérsic index of the pseudobulges does not correlate with B/T , in contrast to classical bulges. Also, the half-light radius of the pseudobulge correlates with the scale length of the disk; this is not the case for classical bulges. The correlation of Sérsic index and scale lengths with bulge morphology suggests that secular evolution is creating pseudobulges with low-Sérsic index and that other processes (e.g., major mergers) are responsible for the higher Sérsic index in classical bulges and elliptical galaxies.
The objective of the Phoenix mission is to determine if Mars' polar region can support life. ... more The objective of the Phoenix mission is to determine if Mars' polar region can support life. Since liquid water is a basic ingredient for life, as we know it, an important goal of the mission is to determine if liquid water exists at the landing site. It is believed that a layer of Martian soil preserves ice by forming a barrier against high temperatures and sublimation, but that exposed ice sublimates without the formation of the liquid phase. Here we show possible independent physical and thermodynamical evidence that besides ice, liquid saline water exists in areas disturbed by the Phoenix Lander. Moreover, we show that the thermodynamics of freeze‐thaw cycles can lead to the formation of saline solutions with freezing temperatures lower than current summer ground temperatures on the Phoenix landing site on Mars' Arctic. Thus, we hypothesize that liquid saline water might occur where ground ice exists near the Martian surface. The ideas and results presented in this artic...
The northern Afar depression of eastern Ethiopia constitutes a young and active rift of the Earth... more The northern Afar depression of eastern Ethiopia constitutes a young and active rift of the Earth's crust, with characters similar to those of oceanic rifts; it can be considered a continuation of the Red Sea rift. We report here on the geochemistry of a Fe-Mn-Ba deposit formed about 200,000 years ago when the Afar Rift was submerged as a branch of the Red Sea. The deposit is associated with fossil coral reefs and is underlain by a submarine basaltic formation. The deposit consists of Fe-rich basal layers with goethite and nontronite as principal constituents overlain by Mn-rich strata which at some levels approach a pure pyrolusite ore. Some of the Mn-rich layers are characterized by high contents of Ba (up to about 6 percent) in the form of crystals of strontiobarite containing up to 12 percent SrSO4 in solid solution. The concentration of Ni, Co, Cr and Cu both in the Fe-rich and Mn-rich layers is very low when compared with marine sedimentary Fe-Mn deposits. The U and Th isotopic chemistry of samples from the deposit indicate that the Fe and Mn minerals were not deposited from normal sea water. The data suggest that the deposit was formed as a result of submarine hydrothermal activity whereby solutions rich in Fe, Mn, Ba, Si and other elements were injected through the sea floor and fractional precipitation of these elements followed. The Afar deposits have strong similarities to the hot brine metalliferous deposits from the Red Sea and to deposits from active oceanic rifts, especially the East Pacific Rise.
The Laurentide Ice Sheet (LIS) occupied a large part of North-America during the late Pleistocene... more The Laurentide Ice Sheet (LIS) occupied a large part of North-America during the late Pleistocene. Determining the proper surface geometry and elevation of the LIS is of central importance to estimate global changes in sea-level and atmospheric circulation patterns during the late Pleistocene and Holocene. Despite largely disappearing from the landscape during the late Holocene, LIS remnants are found in the Penny and Barnes ice caps on Baffin Island (Canada) and ongoing permafrost degradation has been exposing relics of the LIS buried along its northern margin since the late Pleistocene. Here, we use the δO records of six LIS remnants and the late Pleistocene δO-elevation relation to establish ice elevation in their source area during the last glacial maximum (LGM). Contrary to some modeled reconstructions, our findings indicate an asymmetric LIS topography with higher ice on Keewatin Dome (~3200 m) and thinner ice in the prairies along the Plains divide (1700-2100 m) during LGM. T...
Proceedings of the National Academy of Sciences of the United States of America, Jun 16, 2017
We present a revised and extended high Arctic air temperature reconstruction from a single proxy ... more We present a revised and extended high Arctic air temperature reconstruction from a single proxy that spans the past ∼12,000 y (up to 2009 CE). Our reconstruction from the Agassiz ice cap (Ellesmere Island, Canada) indicates an earlier and warmer Holocene thermal maximum with early Holocene temperatures that are 4-5 °C warmer compared with a previous reconstruction, and regularly exceed contemporary values for a period of ∼3,000 y. Our results show that air temperatures in this region are now at their warmest in the past 6,800-7,800 y, and that the recent rate of temperature change is unprecedented over the entire Holocene. The warmer early Holocene inferred from the Agassiz ice core leads to an estimated ∼1 km of ice thinning in northwest Greenland during the early Holocene using the Camp Century ice core. Ice modeling results show that this large thinning is consistent with our air temperature reconstruction. The modeling results also demonstrate the broader significance of the en...
Because of snow drifting, two time series of any variable derived from two adjacent ice cores wil... more Because of snow drifting, two time series of any variable derived from two adjacent ice cores will differ considerably. The size and statistical nature of this noise element is discussed for two kinds of measured substance. A theory is developed and compared to data from Greenland and Canadian Arctic ice cores. In case 1, the measured substance can diffuse and the seasonal cycle degrade with time and depth, e.g. δ(18O). In case 2, the measured substance cannot diffuse, e.g. microparticles. The case 2 time series contain drift noise proportional to that in the accumulation series. For accumulation series, the spectral power is concentrated at the high frequencies, i.e. is “blue”. Such noise can be easily reduced by taking relatively short time averages. The noise in the case 1 time series, however, starts out “blue” but quickly diffuses to have a “red” character with significant power at longer wavelengths, and many decades of such series must be averaged to reduce the noise level. B...
■ COMPARISON WITH EMISSION ESTIMATES INSTEAD OF MODEL OUTPUTS Zhang and Kang focus on our suggest... more ■ COMPARISON WITH EMISSION ESTIMATES INSTEAD OF MODEL OUTPUTS Zhang and Kang focus on our suggestion that current estimates of Hg emissions from Colonial and Gold Rush mining are erroneously high. 1 They propose that comparison of the Mount Logan Hg T flux record to modeled atmospheric Hg concentrations or atmospheric deposition, as shown in Figure 1 of their comment, would be more appropriate than our comparison to emission estimates. The global Hg model they highlight uses the same emission estimates to force a 7-reservoir box model, with exchanges between reservoirs governed by first-order rate constants that are constrained by limited modern-day observations. 2 We chose to compare the Mount Logan Hg T record with the emission estimates to avoid further uncertainty associated with the model. We note that the Mount Logan Hg T record returns to background-level fluxes immediately following the Gold Rush, which is inconsistent with both the global Hg model and the assertion by Zhang and Kang that atmospheric Hg levels are cumulative over half a century. Even if the Mount Logan Hg T record is compared with the global Hg model outputs, our suggestion of erroneously high anthropogenic Hg emission estimates from Colonial and Gold Rush mining remains, as shown in Figure 1 of Zhang and Kang. This suggestion is also made in a recent compilation of 22 lake sediment Hg records from around the world 3 and in chemical modeling of the Colonial silver ore mining process. 4
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Papers by David Fisher