We present the first high-resolution images of CSWA 31, a gravitational lens system observed as p... more We present the first high-resolution images of CSWA 31, a gravitational lens system observed as part of the SLUGS (Sloan Lenses Unravelled by Gemini Studies) program. These systems exhibit complex image structure with the potential to strongly constrain the mass distribution of the massive lens galaxies, as well as the complex morphology of the sources. In this paper, we describe
The Planetary Nebula Spectrograph (PN.S) was designed specifically to measure the shifted wavelen... more The Planetary Nebula Spectrograph (PN.S) was designed specifically to measure the shifted wavelength (and hence velocity) of the 5007{AA} [OIII] emission line that dominates the spectra of PNe. The PN.S observations for this survey were carried out on the William Herschel Telescope (WHT) in La Palma on two runs: 2002 October 8-13 and 2003 September 29-October 5. (1 data file).
Received too late, Accepted even later Abstract. We present the catalogue of a wide-field CFHT/WH... more Received too late, Accepted even later Abstract. We present the catalogue of a wide-field CFHT/WHT spectroscopic survey of the lensing cluster Cl0024+1654 at z = 0.395. This catalogue contains 618 new spectra, of which 581 have identified redshifts. Adding redshifts available from the literature, the final catalogue contains data for 687 objects with redshifts identified for 650 of them. 295
The large-scale structure in the distribution of galaxies is thought to arise from the gravitatio... more The large-scale structure in the distribution of galaxies is thought to arise from the gravitational instability of small fluctuations in the initial density field of the Universe. A key test of this hypothesis is that forming superclusters of galaxies should generate a systematic infall of other galaxies. This would be evident in the pattern of recessional velocities, causing an anisotropy in the inferred spatial clustering of galaxies. Here we report a precise measurement of this clustering, using the redshifts of more than 141,000 galaxies from the two-degree-field (2dF) galaxy redshift survey. We determine the parameter  ¼ ⍀ 0:6 =b ¼ 0:43 Ϯ 0:07, where ⍀ is the total mass-density parameter of the Universe and b is a measure of the 'bias' of the luminous galaxies in the survey. (Bias is the difference between the clustering of visible galaxies and of the total mass, most of which is dark.) Combined with the anisotropy of the cosmic microwave background, our results favour a low-density Universe with ⍀ Ϸ 0:3.
A new population of extended, luminous globular clusters has recently been discovered in the outs... more A new population of extended, luminous globular clusters has recently been discovered in the outskirts of M31. These objects have luminosities typical of classical globular clusters, but much larger half-light radii. We report the first results from deep ACS imaging of four such clusters, one of which is a newly-discovered example lying at a projected distance of ∼ 60 kpc from M31. Our F606W, F814W colour-magnitude diagrams extend ∼ 3 magnitudes below the horizontal branch level, and clearly demonstrate, for the first time, that all four clusters are composed of 10 Gyr old, metal-poor stellar populations. No evidence for multiple populations is observed. From a comparison with Galactic globular cluster fiducials we estimate metallicities in the range −2.2 [Fe/H] −1.8. The observed horizontal branch morphologies show a clear second parameter effect between the clusters. Preliminary radial luminosity profiles suggest integrated magnitudes in the range −6.6 M V −7.7, near the median value of the globular cluster luminosity function. Our results confirm that these four objects are bona fide old, metal-poor globular clusters, albeit with combined structures and -2luminosities unlike those observed for any other globular clusters in the Local Group or beyond.
This paper presents the results of a comprehensive wide field search for transiting "Hot Jupiter"... more This paper presents the results of a comprehensive wide field search for transiting "Hot Jupiter" planets (gas giant planets with an orbital period 1d≤P≤16d) in the globular cluster 47 Tucanae. Motivated by the detection of the transit in HD209458 and the apparent lack of planetary detections in the core of 47 Tuc by Gilliland and coworkers, this work further addresses the question of giant planet
We present the first results on the history of star formation in the Universe based on the 'cosmi... more We present the first results on the history of star formation in the Universe based on the 'cosmic spectrum', in particular, the volume-averaged, luminosity-weighted, stellar absorption line spectrum of present day galaxies from the 2dF Galaxy Redshift Survey. This method is novel in that unlike previous studies it is not an estimator based on total luminosity density. The cosmic spectrum is fitted with models of population synthesis, tracing the history of star formation prior to the epoch of the observed galaxies, using a method we have developed which decouples continuum and spectral-line variations and is robust against spectrophotometric uncertainties. The cosmic spectrum can only be fitted with models incorporating chemical evolution and indicates there was a peak of star-formation rate in the past of at least three times the current value and that the increase back to z = 1, assuming it scales as (1 + z) β , has a strong upper limit of β < 5. We find in the general case there is some model degeneracy between star formation at low and high redshift. However, if we incorporate previous work on star formation at z < 1 we can put strong upper limits on the star-formation rate at z > 1: e.g., if β > 2 then the SFR for 1 < z < 5 scales as (1 + z) α with α < 2. This is equivalent to stating that no more than 80% of stars in the Universe formed at z > 1. Our results are consistent with the best-fit results from compilations of cosmic SFR estimates based on UV luminosity density, which give 1.8 < β < 2.9 and −1.0 < α < 0.7, and are also consistent with estimates of Ω stars based on the K-band luminosity density.
The ages of stellar populations in 52 elliptical and S0 galaxies in the Coma cluster are investig... more The ages of stellar populations in 52 elliptical and S0 galaxies in the Coma cluster are investigated using a new spectroscopic sample. More than 40% of the S0s are found to have experienced recent star formation in their central regions during the last ∼ 5 Gyrs, while such activity is absent in the ellipticals. Galaxies in this sample have absolute magnitudes in the range −20.5 < M B < −17.5, and the fraction of S0 galaxies with recent star formation is higher at fainter luminosities. The observed luminosity range of S0 galaxies with signs of recent star formation activity is consistent with them being the descendants of typical star-forming spirals at intermediate redshift whose star formation has been halted as a consequence of the dense environment.
1 2 DYNAMICS OF THE M87 GLOBULAR CLUSTER SYSTEM ABSTRACT We present a dynamical analysis of the g... more 1 2 DYNAMICS OF THE M87 GLOBULAR CLUSTER SYSTEM ABSTRACT We present a dynamical analysis of the globular cluster system associated with M87 (= NGC 4486), the cD galaxy near the dynamical center of the Virgo cluster. The analysis utilizes a new spectroscopic and photometric database which is described in a companion paper ). Using a sample of 278 globular clusters with measured radial velocities and metallicities, and new surface density profiles based on wide-field Washington photometry, we study the dynamics of the M87 globular cluster system both globally -for the entire cluster sample -and separately -for the metal-rich and metal-poor globular cluster samples. This constitutes the largest sample of radial velocities for pure Population II tracers yet assembled for any galaxy. Our principal findings are summarized as follows:
Intracluster stellar populations are a natural result of tidal interactions in galaxy clusters. M... more Intracluster stellar populations are a natural result of tidal interactions in galaxy clusters. Measuring these populations is difficult, but important for understanding the assembly of the most massive galaxies. The Coma cluster of galaxies is one of the nearest truly massive galaxy clusters, and is host to a correspondingly large system of globular clusters (GCs). We use imaging from the HST/ACS Coma Cluster Survey to present the first definitive detection of a large population of intracluster GCs (IGCs) that fills the Coma cluster core and is not associated with individual galaxies. The GC surface density profile around the central massive elliptical galaxy, NGC 4874, is dominated at large radii by a population of IGCs that extend to the limit of our data (R < 520 kpc). We estimate that there are 47000 ± 1600 (random) +4000
We present a variable star catalog of an extensive ground-based wide-field variability survey in ... more We present a variable star catalog of an extensive ground-based wide-field variability survey in the globular cluster ω Centauri. Using the ANU 40-inch (1m) telescope at Siding Spring Observatory, the cluster was observed with a 52 ′ ×52 ′ (0.75 deg 2 ) field for 25 nights. A total of 187 variable stars were identified in the field, 81 of which are new discoveries. This work comprises the widest field variability survey yet undertaken for this cluster. Here we present the V+R lightcurves and preliminary analysis of the detected variable stars, comprising 58 eclipsing binaries, 69 RR Lyrae stars, 36 long period variables (P≥2d) and 24 miscellaneous pulsators including 15 SX Phoenicis stars and two Type II Cepheids.
We present new radial velocities for 87 globular clusters around the elliptical galaxy NGC 4472, ... more We present new radial velocities for 87 globular clusters around the elliptical galaxy NGC 4472, and combine these with our previously published data to create a data set of velocities for 144 globular clusters around NGC 4472. We utilize this data set to analyze the kinematics of the NGC 4472 globular cluster system. The new
We present the results of a comprehensive search for stellar variability in the globular cluster ... more We present the results of a comprehensive search for stellar variability in the globular cluster 47 Tucanae. Using the Mount Stromlo 40-inch (1m) telescope at Siding Spring Observatory and a combined V+R filter, we have detected 100 variable stars across a 52×52 ′ field centered on the cluster. The main aim of this project is to search for transiting 'Hot Jupiter' planets in this cluster, the results of which shall be discussed in a separate paper. Here we present the V+R lightcurves and preliminary investigations of the detected variable stars, which comprise 28 Eclipsing Binaries (21 contact binaries and 7 detached systems), 45 RR Lyrae stars (41 of which belong to the Small Magellanic Cloud and four seemingly to the Galactic Halo), and 20 K-giant Long Period Variables (LPVs).
A new kinematic and dynamic study of the halo of the giant elliptical galaxy NGC 5128 is presente... more A new kinematic and dynamic study of the halo of the giant elliptical galaxy NGC 5128 is presented. From a spectroscopically confirmed sample of 340 globular clusters and 780 planetary nebulae, the rotation amplitude, rotation axis, velocity dispersion, and total dynamical mass are determined for the halo of NGC 5128. The globular cluster kinematics were searched for both radial dependence and metallicity dependence by subdividing the globular cluster sample into 158 metal-rich ([Fe/H]> −1.0) and 178 metal-poor ([Fe/H]< −1.0) globular clusters. Our results show that the kinematics of the metal-rich and metal-poor subpopulations are quite similar: over a projected radius of 0 − 50 kpc, the mean rotation amplitudes are 47 ± 15 and 31 ± 14 km s −1 for the metal-rich and metalpoor populations, respectively. There is a indication within 0 − 5 kpc that the metal-poor clusters have a lower rotation signal than in the outer regions of the galaxy. The rotation axis shows an interesting twist at 5 kpc, agreeing with the zero-velocity curve presented by Peng and coworkers. Within 5 kpc, both metal-rich and metal-poor populations have a rotation axis nearly parallel to the north-south direction, which is 0 o , while beyond 5 kpc the rotation axis twists ∼ 180 o . The velocity dispersion displays a steady increase with galactocentric radius for both metallicity populations, with means of 111 ± 6 and 117 ± 6 km s −1 within a projected radius of 15 kpc for the metal-rich and metal-poor populations; however, the outermost regions suffer from low number statistics and spatial biases. The planetary nebula kinematics are slightly different. Out to a projected radius of 90 kpc from the center of NGC 5128, the planetary nebulae have a higher rotation amplitude of 76 ± 6 km s −1 , and a rotation axis of 170 ± 5 o east of north, with no significant radial deviation in either determined quantity. The velocity dispersion decreases with galactocentric distance. The total mass of NGC 5128 is found using the tracer mass estimator, described by Evans et al., to determine the mass supported by internal random motions and the spherical component of the Jeans equation to determine the mass supported by rotation. We find a total mass of 1.0 ± 0.2 × 10 12 M ⊙ from the planetary nebula data extending to a projected radius of 90 kpc. The similar kinematics of the metal-rich and metal-poor globular clusters allow us to combine the two subpopulations -3to determine an independent estimate of the total mass, giving 1.3 ± 0.5 × 10 12 M ⊙ out to a projected radius of 50 kpc. Lastly, we publish a new and homogeneous catalog of known globular clusters in NGC 5128. This catalog combines all previous definitive cluster identifications from radial velocity studies and HST imaging studies, as well as 80 new globular clusters with radial velocities from a study of M.A. Beasley et al. (in preparation).
We constrain fν ≡ Ων /Ωm, the fractional contribution of neutrinos to the total mass density in t... more We constrain fν ≡ Ων /Ωm, the fractional contribution of neutrinos to the total mass density in the Universe, by comparing the power spectrum of fluctuations derived from the 2dF Galaxy Redshift Survey with power spectra for models with four components: baryons, cold dark matter, massive neutrinos and a cosmological constant. Adding constraints from independent cosmological probes we find fν < 0.13 (at 95% confidence) for a prior of 0.1 < Ωm < 0.5, and assuming the scalar spectral index n = 1. This translates to an upper limit on the total neutrino mass mν,tot < 1.8 eV for 'concordance' values of Ωm and the Hubble constant. Very similar results are obtained with a prior on Ωm from Type Ia supernovae surveys, and with marginalization over n.
Monthly Notices of the Royal Astronomical Society, 2004
We analyse the observed correlation between galaxy environment and Hα emission line strength, usi... more We analyse the observed correlation between galaxy environment and Hα emission line strength, using volume-limited samples and group catalogues of 24968 galaxies at 0.05 < z < 0.095, drawn from the 2dF Galaxy Redshift Survey (M bJ < −19.5) and the Sloan Digital Sky Survey (M r < −20.6). We characterise the environment by 1) Σ 5 , the surface number density of galaxies determined by the projected distance to the 5 th nearest neighbour; and 2) ρ 1.1 and ρ 5.5 , three-dimensional density estimates obtained by convolving the galaxy distribution with Gaussian kernels of dispersion 1.1 Mpc and 5.5 Mpc, respectively. We find that star-forming and quiescent galaxies form two distinct populations, as characterised by their Hα equivalent width, W 0 (Hα). The relative numbers of star-forming and quiescent galaxies varies strongly and continuously with local density. However, the distribution of W 0 (Hα) amongst the star-forming population is independent of environment. The fraction of star-forming galaxies shows strong sensitivity to the density on large scales, ρ 5.5 , which is likely independent of the trend with local density, ρ 1.1 . We use two differently-selected group catalogues to demonstrate that the correlation with galaxy density is approximately independent of group velocity dispersion, for σ = 200-1000 km s −1 . Even in the lowest density environments, no more than ∼ 70 per cent of galaxies show significant Hα emission. Based on these results, we conclude that the present-day correlation between star formation rate and environment is a result of short-timescale mechanisms that take place preferentially at high redshift, such as starbursts induced by galaxy-galaxy interactions.
Monthly Notices of the Royal Astronomical Society, 2004
Complementary one-, two-, and three-dimensional tests for detecting the presence of substructure ... more Complementary one-, two-, and three-dimensional tests for detecting the presence of substructure in clusters of galaxies are applied to recently obtained data from the 2dF Galaxy Redshift Survey. The sample of 25 clusters used in this study includes 16 clusters not previously investigated for substructure. Substructure is detected at or greater than the 99% CL level in at least one test for 21 of the 25 clusters studied here. From the results, it appears that low richness clusters commonly contain subclusters participating in mergers. About half of the clusters have two or more components within 0.5 h −1 Mpc of the cluster centroid, and at least three clusters (Abell 1139, Abell 1663, and Abell S333) exhibit velocity-position characteristics consistent with the presence of possible cluster rotation, shear, or infall dynamics. The geometry of certain features is consistent with influence by the host supercluster environments. In general, our results support the hypothesis that low richness clusters relax to structureless equilibrium states on very long dynamical time scales (if at all).
Monthly Notices of the Royal Astronomical Society, 2004
We measure the clustering of galaxy groups in the 2dFGRS Percolation-Inferred Galaxy Group (2PIGG... more We measure the clustering of galaxy groups in the 2dFGRS Percolation-Inferred Galaxy Group (2PIGG) catalogue. The 2PIGG sample has 28 877 groups with at least two members. The clustering amplitude of the full 2PIGG catalogue is weaker than that of 2dFGRS galaxies, in agreement with theoretical predictions. We have subdivided the 2PIGG catalogue into samples that span a factor of ≈ 25 in median total luminosity. Our correlation function measurements span an unprecedented range of clustering strengths, connecting the regimes probed by groups fainter than L * galaxies and rich clusters. There is a steady increase in clustering strength with group luminosity; the most luminous groups are ten times more strongly clustered than the full 2PIGG catalogue. We demonstrate that the 2PIGG results are in very good agreement with the clustering of groups expected in the ΛCDM model.
We present the first high-resolution images of CSWA 31, a gravitational lens system observed as p... more We present the first high-resolution images of CSWA 31, a gravitational lens system observed as part of the SLUGS (Sloan Lenses Unravelled by Gemini Studies) program. These systems exhibit complex image structure with the potential to strongly constrain the mass distribution of the massive lens galaxies, as well as the complex morphology of the sources. In this paper, we describe
The Planetary Nebula Spectrograph (PN.S) was designed specifically to measure the shifted wavelen... more The Planetary Nebula Spectrograph (PN.S) was designed specifically to measure the shifted wavelength (and hence velocity) of the 5007{AA} [OIII] emission line that dominates the spectra of PNe. The PN.S observations for this survey were carried out on the William Herschel Telescope (WHT) in La Palma on two runs: 2002 October 8-13 and 2003 September 29-October 5. (1 data file).
Received too late, Accepted even later Abstract. We present the catalogue of a wide-field CFHT/WH... more Received too late, Accepted even later Abstract. We present the catalogue of a wide-field CFHT/WHT spectroscopic survey of the lensing cluster Cl0024+1654 at z = 0.395. This catalogue contains 618 new spectra, of which 581 have identified redshifts. Adding redshifts available from the literature, the final catalogue contains data for 687 objects with redshifts identified for 650 of them. 295
The large-scale structure in the distribution of galaxies is thought to arise from the gravitatio... more The large-scale structure in the distribution of galaxies is thought to arise from the gravitational instability of small fluctuations in the initial density field of the Universe. A key test of this hypothesis is that forming superclusters of galaxies should generate a systematic infall of other galaxies. This would be evident in the pattern of recessional velocities, causing an anisotropy in the inferred spatial clustering of galaxies. Here we report a precise measurement of this clustering, using the redshifts of more than 141,000 galaxies from the two-degree-field (2dF) galaxy redshift survey. We determine the parameter  ¼ ⍀ 0:6 =b ¼ 0:43 Ϯ 0:07, where ⍀ is the total mass-density parameter of the Universe and b is a measure of the 'bias' of the luminous galaxies in the survey. (Bias is the difference between the clustering of visible galaxies and of the total mass, most of which is dark.) Combined with the anisotropy of the cosmic microwave background, our results favour a low-density Universe with ⍀ Ϸ 0:3.
A new population of extended, luminous globular clusters has recently been discovered in the outs... more A new population of extended, luminous globular clusters has recently been discovered in the outskirts of M31. These objects have luminosities typical of classical globular clusters, but much larger half-light radii. We report the first results from deep ACS imaging of four such clusters, one of which is a newly-discovered example lying at a projected distance of ∼ 60 kpc from M31. Our F606W, F814W colour-magnitude diagrams extend ∼ 3 magnitudes below the horizontal branch level, and clearly demonstrate, for the first time, that all four clusters are composed of 10 Gyr old, metal-poor stellar populations. No evidence for multiple populations is observed. From a comparison with Galactic globular cluster fiducials we estimate metallicities in the range −2.2 [Fe/H] −1.8. The observed horizontal branch morphologies show a clear second parameter effect between the clusters. Preliminary radial luminosity profiles suggest integrated magnitudes in the range −6.6 M V −7.7, near the median value of the globular cluster luminosity function. Our results confirm that these four objects are bona fide old, metal-poor globular clusters, albeit with combined structures and -2luminosities unlike those observed for any other globular clusters in the Local Group or beyond.
This paper presents the results of a comprehensive wide field search for transiting "Hot Jupiter"... more This paper presents the results of a comprehensive wide field search for transiting "Hot Jupiter" planets (gas giant planets with an orbital period 1d≤P≤16d) in the globular cluster 47 Tucanae. Motivated by the detection of the transit in HD209458 and the apparent lack of planetary detections in the core of 47 Tuc by Gilliland and coworkers, this work further addresses the question of giant planet
We present the first results on the history of star formation in the Universe based on the 'cosmi... more We present the first results on the history of star formation in the Universe based on the 'cosmic spectrum', in particular, the volume-averaged, luminosity-weighted, stellar absorption line spectrum of present day galaxies from the 2dF Galaxy Redshift Survey. This method is novel in that unlike previous studies it is not an estimator based on total luminosity density. The cosmic spectrum is fitted with models of population synthesis, tracing the history of star formation prior to the epoch of the observed galaxies, using a method we have developed which decouples continuum and spectral-line variations and is robust against spectrophotometric uncertainties. The cosmic spectrum can only be fitted with models incorporating chemical evolution and indicates there was a peak of star-formation rate in the past of at least three times the current value and that the increase back to z = 1, assuming it scales as (1 + z) β , has a strong upper limit of β < 5. We find in the general case there is some model degeneracy between star formation at low and high redshift. However, if we incorporate previous work on star formation at z < 1 we can put strong upper limits on the star-formation rate at z > 1: e.g., if β > 2 then the SFR for 1 < z < 5 scales as (1 + z) α with α < 2. This is equivalent to stating that no more than 80% of stars in the Universe formed at z > 1. Our results are consistent with the best-fit results from compilations of cosmic SFR estimates based on UV luminosity density, which give 1.8 < β < 2.9 and −1.0 < α < 0.7, and are also consistent with estimates of Ω stars based on the K-band luminosity density.
The ages of stellar populations in 52 elliptical and S0 galaxies in the Coma cluster are investig... more The ages of stellar populations in 52 elliptical and S0 galaxies in the Coma cluster are investigated using a new spectroscopic sample. More than 40% of the S0s are found to have experienced recent star formation in their central regions during the last ∼ 5 Gyrs, while such activity is absent in the ellipticals. Galaxies in this sample have absolute magnitudes in the range −20.5 < M B < −17.5, and the fraction of S0 galaxies with recent star formation is higher at fainter luminosities. The observed luminosity range of S0 galaxies with signs of recent star formation activity is consistent with them being the descendants of typical star-forming spirals at intermediate redshift whose star formation has been halted as a consequence of the dense environment.
1 2 DYNAMICS OF THE M87 GLOBULAR CLUSTER SYSTEM ABSTRACT We present a dynamical analysis of the g... more 1 2 DYNAMICS OF THE M87 GLOBULAR CLUSTER SYSTEM ABSTRACT We present a dynamical analysis of the globular cluster system associated with M87 (= NGC 4486), the cD galaxy near the dynamical center of the Virgo cluster. The analysis utilizes a new spectroscopic and photometric database which is described in a companion paper ). Using a sample of 278 globular clusters with measured radial velocities and metallicities, and new surface density profiles based on wide-field Washington photometry, we study the dynamics of the M87 globular cluster system both globally -for the entire cluster sample -and separately -for the metal-rich and metal-poor globular cluster samples. This constitutes the largest sample of radial velocities for pure Population II tracers yet assembled for any galaxy. Our principal findings are summarized as follows:
Intracluster stellar populations are a natural result of tidal interactions in galaxy clusters. M... more Intracluster stellar populations are a natural result of tidal interactions in galaxy clusters. Measuring these populations is difficult, but important for understanding the assembly of the most massive galaxies. The Coma cluster of galaxies is one of the nearest truly massive galaxy clusters, and is host to a correspondingly large system of globular clusters (GCs). We use imaging from the HST/ACS Coma Cluster Survey to present the first definitive detection of a large population of intracluster GCs (IGCs) that fills the Coma cluster core and is not associated with individual galaxies. The GC surface density profile around the central massive elliptical galaxy, NGC 4874, is dominated at large radii by a population of IGCs that extend to the limit of our data (R < 520 kpc). We estimate that there are 47000 ± 1600 (random) +4000
We present a variable star catalog of an extensive ground-based wide-field variability survey in ... more We present a variable star catalog of an extensive ground-based wide-field variability survey in the globular cluster ω Centauri. Using the ANU 40-inch (1m) telescope at Siding Spring Observatory, the cluster was observed with a 52 ′ ×52 ′ (0.75 deg 2 ) field for 25 nights. A total of 187 variable stars were identified in the field, 81 of which are new discoveries. This work comprises the widest field variability survey yet undertaken for this cluster. Here we present the V+R lightcurves and preliminary analysis of the detected variable stars, comprising 58 eclipsing binaries, 69 RR Lyrae stars, 36 long period variables (P≥2d) and 24 miscellaneous pulsators including 15 SX Phoenicis stars and two Type II Cepheids.
We present new radial velocities for 87 globular clusters around the elliptical galaxy NGC 4472, ... more We present new radial velocities for 87 globular clusters around the elliptical galaxy NGC 4472, and combine these with our previously published data to create a data set of velocities for 144 globular clusters around NGC 4472. We utilize this data set to analyze the kinematics of the NGC 4472 globular cluster system. The new
We present the results of a comprehensive search for stellar variability in the globular cluster ... more We present the results of a comprehensive search for stellar variability in the globular cluster 47 Tucanae. Using the Mount Stromlo 40-inch (1m) telescope at Siding Spring Observatory and a combined V+R filter, we have detected 100 variable stars across a 52×52 ′ field centered on the cluster. The main aim of this project is to search for transiting 'Hot Jupiter' planets in this cluster, the results of which shall be discussed in a separate paper. Here we present the V+R lightcurves and preliminary investigations of the detected variable stars, which comprise 28 Eclipsing Binaries (21 contact binaries and 7 detached systems), 45 RR Lyrae stars (41 of which belong to the Small Magellanic Cloud and four seemingly to the Galactic Halo), and 20 K-giant Long Period Variables (LPVs).
A new kinematic and dynamic study of the halo of the giant elliptical galaxy NGC 5128 is presente... more A new kinematic and dynamic study of the halo of the giant elliptical galaxy NGC 5128 is presented. From a spectroscopically confirmed sample of 340 globular clusters and 780 planetary nebulae, the rotation amplitude, rotation axis, velocity dispersion, and total dynamical mass are determined for the halo of NGC 5128. The globular cluster kinematics were searched for both radial dependence and metallicity dependence by subdividing the globular cluster sample into 158 metal-rich ([Fe/H]> −1.0) and 178 metal-poor ([Fe/H]< −1.0) globular clusters. Our results show that the kinematics of the metal-rich and metal-poor subpopulations are quite similar: over a projected radius of 0 − 50 kpc, the mean rotation amplitudes are 47 ± 15 and 31 ± 14 km s −1 for the metal-rich and metalpoor populations, respectively. There is a indication within 0 − 5 kpc that the metal-poor clusters have a lower rotation signal than in the outer regions of the galaxy. The rotation axis shows an interesting twist at 5 kpc, agreeing with the zero-velocity curve presented by Peng and coworkers. Within 5 kpc, both metal-rich and metal-poor populations have a rotation axis nearly parallel to the north-south direction, which is 0 o , while beyond 5 kpc the rotation axis twists ∼ 180 o . The velocity dispersion displays a steady increase with galactocentric radius for both metallicity populations, with means of 111 ± 6 and 117 ± 6 km s −1 within a projected radius of 15 kpc for the metal-rich and metal-poor populations; however, the outermost regions suffer from low number statistics and spatial biases. The planetary nebula kinematics are slightly different. Out to a projected radius of 90 kpc from the center of NGC 5128, the planetary nebulae have a higher rotation amplitude of 76 ± 6 km s −1 , and a rotation axis of 170 ± 5 o east of north, with no significant radial deviation in either determined quantity. The velocity dispersion decreases with galactocentric distance. The total mass of NGC 5128 is found using the tracer mass estimator, described by Evans et al., to determine the mass supported by internal random motions and the spherical component of the Jeans equation to determine the mass supported by rotation. We find a total mass of 1.0 ± 0.2 × 10 12 M ⊙ from the planetary nebula data extending to a projected radius of 90 kpc. The similar kinematics of the metal-rich and metal-poor globular clusters allow us to combine the two subpopulations -3to determine an independent estimate of the total mass, giving 1.3 ± 0.5 × 10 12 M ⊙ out to a projected radius of 50 kpc. Lastly, we publish a new and homogeneous catalog of known globular clusters in NGC 5128. This catalog combines all previous definitive cluster identifications from radial velocity studies and HST imaging studies, as well as 80 new globular clusters with radial velocities from a study of M.A. Beasley et al. (in preparation).
We constrain fν ≡ Ων /Ωm, the fractional contribution of neutrinos to the total mass density in t... more We constrain fν ≡ Ων /Ωm, the fractional contribution of neutrinos to the total mass density in the Universe, by comparing the power spectrum of fluctuations derived from the 2dF Galaxy Redshift Survey with power spectra for models with four components: baryons, cold dark matter, massive neutrinos and a cosmological constant. Adding constraints from independent cosmological probes we find fν < 0.13 (at 95% confidence) for a prior of 0.1 < Ωm < 0.5, and assuming the scalar spectral index n = 1. This translates to an upper limit on the total neutrino mass mν,tot < 1.8 eV for 'concordance' values of Ωm and the Hubble constant. Very similar results are obtained with a prior on Ωm from Type Ia supernovae surveys, and with marginalization over n.
Monthly Notices of the Royal Astronomical Society, 2004
We analyse the observed correlation between galaxy environment and Hα emission line strength, usi... more We analyse the observed correlation between galaxy environment and Hα emission line strength, using volume-limited samples and group catalogues of 24968 galaxies at 0.05 < z < 0.095, drawn from the 2dF Galaxy Redshift Survey (M bJ < −19.5) and the Sloan Digital Sky Survey (M r < −20.6). We characterise the environment by 1) Σ 5 , the surface number density of galaxies determined by the projected distance to the 5 th nearest neighbour; and 2) ρ 1.1 and ρ 5.5 , three-dimensional density estimates obtained by convolving the galaxy distribution with Gaussian kernels of dispersion 1.1 Mpc and 5.5 Mpc, respectively. We find that star-forming and quiescent galaxies form two distinct populations, as characterised by their Hα equivalent width, W 0 (Hα). The relative numbers of star-forming and quiescent galaxies varies strongly and continuously with local density. However, the distribution of W 0 (Hα) amongst the star-forming population is independent of environment. The fraction of star-forming galaxies shows strong sensitivity to the density on large scales, ρ 5.5 , which is likely independent of the trend with local density, ρ 1.1 . We use two differently-selected group catalogues to demonstrate that the correlation with galaxy density is approximately independent of group velocity dispersion, for σ = 200-1000 km s −1 . Even in the lowest density environments, no more than ∼ 70 per cent of galaxies show significant Hα emission. Based on these results, we conclude that the present-day correlation between star formation rate and environment is a result of short-timescale mechanisms that take place preferentially at high redshift, such as starbursts induced by galaxy-galaxy interactions.
Monthly Notices of the Royal Astronomical Society, 2004
Complementary one-, two-, and three-dimensional tests for detecting the presence of substructure ... more Complementary one-, two-, and three-dimensional tests for detecting the presence of substructure in clusters of galaxies are applied to recently obtained data from the 2dF Galaxy Redshift Survey. The sample of 25 clusters used in this study includes 16 clusters not previously investigated for substructure. Substructure is detected at or greater than the 99% CL level in at least one test for 21 of the 25 clusters studied here. From the results, it appears that low richness clusters commonly contain subclusters participating in mergers. About half of the clusters have two or more components within 0.5 h −1 Mpc of the cluster centroid, and at least three clusters (Abell 1139, Abell 1663, and Abell S333) exhibit velocity-position characteristics consistent with the presence of possible cluster rotation, shear, or infall dynamics. The geometry of certain features is consistent with influence by the host supercluster environments. In general, our results support the hypothesis that low richness clusters relax to structureless equilibrium states on very long dynamical time scales (if at all).
Monthly Notices of the Royal Astronomical Society, 2004
We measure the clustering of galaxy groups in the 2dFGRS Percolation-Inferred Galaxy Group (2PIGG... more We measure the clustering of galaxy groups in the 2dFGRS Percolation-Inferred Galaxy Group (2PIGG) catalogue. The 2PIGG sample has 28 877 groups with at least two members. The clustering amplitude of the full 2PIGG catalogue is weaker than that of 2dFGRS galaxies, in agreement with theoretical predictions. We have subdivided the 2PIGG catalogue into samples that span a factor of ≈ 25 in median total luminosity. Our correlation function measurements span an unprecedented range of clustering strengths, connecting the regimes probed by groups fainter than L * galaxies and rich clusters. There is a steady increase in clustering strength with group luminosity; the most luminous groups are ten times more strongly clustered than the full 2PIGG catalogue. We demonstrate that the 2PIGG results are in very good agreement with the clustering of groups expected in the ΛCDM model.
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Papers by Terry Bridges