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[show abstract]
[hide abstract]
ABSTRACT: From two very simple axioms: (1) that AGN activity traces spheroid formation,
and (2) that the cosmic star-formation history is dominated by spheroid
formation at high redshift, we derive simple expressions for the star-formation
histories of spheroids and discs, and their implied metal enrichment histories.
Adopting a Baldry-Glazebrook initial mass function we use these relations and
apply PEGASE.2 to predict the z=0 cosmic spectral energy distributions (CSEDs)
of spheroids and discs. The model predictions compare favourably to the
dust-corrected CSED recently reported by the Galaxy And Mass Assembly (GAMA)
team from the FUV through to the K band. The model also provides a reasonable
fit to the total stellar mass contained within spheroid and disc structures as
recently reported by the Millennium Galaxy Catalogue team. Three interesting
inferences can be made following our axioms: (1) there is a transition redshift
at z ~ 1.7 at which point the Universe switches from what we refer to as "hot
mode evolution" (i.e., spheroid formation/growth via mergers and/or collapse)
to what we term "cold mode evolution" (i.e., disc formation/growth via gas
infall and minor mergers); (2) there is little or no need for any
pre-enrichment prior to the main phase of star-formation; (3) in the present
Universe mass-loss is fairly evenly balanced with star-formation holding the
integrated stellar mass density close to a constant value.
The model provides a simple prediction of the energy output from spheroid and
disc projenitors, the build-up of spheroid and disc mass, and the mean
metallicity enrichment of the Universe.
01/2013;
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Lee S. Kelvin,
Simon P. Driver,
Aaron S. G. Robotham,
David T. Hill,
Mehmet Alpaslan,
Ivan K. Baldry,
Steven P. Bamford,
Joss Bland-Hawthorn,
Sarah Brough,
Alister W. Graham,
Boris Häussler,
Andrew M. Hopkins,
Jochen Liske,
Jon Loveday,
Peder Norberg, Steven Phillipps,
Cristina C. Popescu,
Matthew Prescott,
Edward N. Taylor,
Richard J. Tuffs
[show abstract]
[hide abstract]
ABSTRACT: We present single-Sérsic two-dimensional (2D) model fits to 167
600 galaxies modelled independently in the ugrizYJHK bandpasses using
reprocessed Sloan Digital Sky Survey Data Release Seven (SDSS DR7) and
UKIRT Infrared Deep Sky Survey Large Area Survey imaging data available
from the Galaxy And Mass Assembly (GAMA) data base. In order to
facilitate this study we developed Structural Investigation of Galaxies
via Model Analysis (SIGMA), an R wrapper around several contemporary
astronomy software packages including SOURCE EXTRACTOR, PSF EXTRACTOR
and GALFIT 3. SIGMA produces realistic 2D model fits to galaxies,
employing automatic adaptive background subtraction and empirical point
spread function measurements on the fly for each galaxy in GAMA. Using
these results, we define a common coverage area across the three GAMA
regions containing 138 269 galaxies. We provide Sérsic magnitudes
truncated at 10re which show good agreement with SDSS
Petrosian and GAMA photometry for low Sérsic index systems (n
< 4), and much improved photometry for high Sérsic index
systems (n > 4), recovering as much as Δm= 0.5 mag in the r
band. We employ a K-band Sérsic index/u-r colour relation to
delineate the massive (n > ˜2) early-type galaxies (ETGs) from
the late-type galaxies (LTGs). The mean Sérsic index of these
ETGs shows a smooth variation with wavelength, increasing by 30 per cent
from g through K. LTGs exhibit a more extreme change in Sérsic
index, increasing by 52 per cent across the same range. In addition,
ETGs and LTGs exhibit a 38 and 25 per cent decrease, respectively, in
half-light radius from g through K. These trends are shown to arise due
to the effects of dust attenuation and stellar population/metallicity
gradients within galaxy populations.
Monthly Notices of the Royal Astronomical Society 03/2012; 421:1007-1039. · 4.90 Impact Factor
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Lee S. Kelvin,
Simon P. Driver,
Aaron S. G. Robotham,
David T. Hill,
Mehmet Alpaslan,
Ivan K. Baldry,
Steven P. Bamford,
Joss Bland-Hawthorn,
Sarah Brough,
Alister W. Graham,
Boris Häussler,
Andrew M. Hopkins,
Jochen Liske,
Jon Loveday,
Peder Norberg, Steven Phillipps,
Cristina C. Popescu,
Matthew Prescott,
Edward N. Taylor,
Richard J. Tuffs
[show abstract]
[hide abstract]
ABSTRACT: We present single-S\'ersic two-dimensional model fits to 167,600 galaxies
modelled independently in the ugrizYJHK bandpasses using reprocessed Sloan
Digital Sky Survey Data Release Seven (SDSS DR7) and UKIRT Infrared Deep Sky
Survey Large Area Survey (UKIDSS-LAS) imaging data available from the GAMA
database. In order to facilitate this study we developed SIGMA, an R wrapper
around several contemporary astronomy software packages including Source
Extractor, PSF Extractor and GALFIT 3. SIGMA produces realistic 2D model fits
to galaxies, employing automatic adaptive background subtraction and empirical
PSF measurements on the fly for each galaxy in GAMA. Using these results, we
define a common coverage area across the three GAMA regions containing 138,269
galaxies. We provide S\'ersic magnitudes truncated at 10 re which show good
agreement with SDSS Petrosian and GAMA photometry for low S\'ersic index
systems (n < 4), and much improved photometry for high S\'ersic index systems
(n > 4), recovering as much as \Delta m = 0.5 magnitudes in the r band. We
employ a K band S\'ersic index/u - r colour relation to delineate the massive
(n > ~2) early-type galaxies (ETGs) from the late-type galaxies (LTGs). The
mean S\'ersic index of these ETGs shows a smooth variation with wavelength,
increasing by 30% from g through K. LTGs exhibit a more extreme change in
S\'ersic index, increasing by 52% across the same range. In addition, ETGs and
LTGs exhibit a 38% and 25% decrease respectively in half-light radius from g
through K. These trends are shown to arise due to the effects of dust
attenuation and stellar population/metallicity gradients within galaxy
populations.
12/2011;
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[show abstract]
[hide abstract]
ABSTRACT: We explore the variation in stellar population ages for Coma cluster galaxies
as a function of projected cluster-centric distance, using a sample of 362
red-sequence galaxies with high signal-to-noise spectroscopy. The sample spans
a wide range in luminosity (0.02-4 L*) and extends from the cluster core to
near the virial radius. We find a clear distinction in the observed trends of
the giant and dwarf galaxies. The ages of red-sequence giants are primarily
determined by galaxy mass, with only weak modulation by environment, in the
sense that galaxies at larger cluster-centric distance are slightly younger.
For red-sequence dwarfs (with mass <10^10 Msun), the roles of mass and
environment as predictors of age are reversed: there is little dependence on
mass, but strong trends with projected cluster-centric radius are observed. The
average age of dwarfs at the 2.5 Mpc limit of our sample is approximately half
that of dwarfs near the cluster centre. The gradient in dwarf galaxy ages is a
global cluster-centric trend, and is not driven by the ongoing merger of the
NGC 4839 group to the south west of Coma. We interpret these results using
environmental histories extracted from the Millennium Simulation for members of
massive clusters. Hierarchical cluster assembly naturally leads to trends in
the accretion times of galaxies as a function of projected cluster-centric
radius. On average, simulated galaxies now located in cluster cores joined
halos above any given mass threshold earlier than those now located in the
outskirts of clusters. We test environmental quenching models, in which star
formation is halted in galaxies when they enter halos of a given mass, or
become satellite galaxies. The models broadly reproduce the gradients observed
in Coma, but for dwarf galaxies the efficiency of environmental quenching must
be very high to match the strong trends observed.
08/2011;
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David T. Hill,
Lee S. Kelvin,
Simon P. Driver,
Aaron S. G. Robotham,
Ewan Cameron,
Nicholas Cross,
Ellen Andrae,
Ivan K. Baldry,
Steven P. Bamford,
Joss Bland-Hawthorn, [......], Steven Phillipps,
Kevin A. Pimbblet,
Cristina C. Popescu,
Matthew Prescott,
Mark Seibert,
Rob G. Sharp,
Will J. Sutherland,
Daniel Thomas,
Richard J. Tuffs,
Elco van Kampen
[show abstract]
[hide abstract]
ABSTRACT: In order to generate credible 0.1–2 μm spectral energy distributions, the Galaxy and Mass Assembly (GAMA) project requires many gigabytes of imaging data from a number of instruments to be reprocessed into a standard format. In this paper, we discuss the software infrastructure we use, and create self-consistent ugrizYJHK photometry for all sources within the GAMA sample. Using UKIDSS and SDSS archive data, we outline the pre-processing necessary to standardize all images to a common zero-point, the steps taken to correct for the seeing bias across the data set and the creation of gigapixel-scale mosaics of the three 4 × 12 deg2 GAMA regions in each filter. From these mosaics, we extract source catalogues for the GAMA regions using elliptical Kron and Petrosian matched apertures. We also calculate Sérsic magnitudes for all galaxies within the GAMA sample using sigma, a galaxy component modelling wrapper for galfit 3. We compare the resultant photometry directly and also calculate the r-band galaxy luminosity function for all photometric data sets to highlight the uncertainty introduced by the photometric method. We find that (1) changing the object detection threshold has a minor effect on the best-fitting Schechter parameters of the overall population (M*± 0.055 mag, α± 0.014, ϕ*± 0.0005 h3 Mpc−3); (2) there is an offset between data sets that use Kron or Petrosian photometry, regardless of the filter; (3) the decision to use circular or elliptical apertures causes an offset in M* of 0.20 mag; (4) the best-fitting Schechter parameters from total-magnitude photometric systems (such as SDSS modelmag or Sérsic magnitudes) have a steeper faint-end slope than photometric systems based upon Kron or Petrosian measurements; and (5) our Universe’s total luminosity density, when calculated using Kron or Petrosian r-band photometry, is underestimated by at least 15 per cent.
Monthly Notices of the Royal Astronomical Society 03/2011; 412(2):765 - 799. · 4.90 Impact Factor
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Eric W. Peng,
Henry C. Ferguson,
Paul Goudfrooij,
Derek Hammer,
John R. Lucey,
Ronald O. Marzke,
Thomas H. Puzia,
David Carter,
Marc Balcells,
Terry Bridges, [......],
Michael J. Hudson,
Ana Matković,
David Merritt,
Bryan W. Miller,
Mustapha Mouhcine, Steven Phillipps,
Ray Sharples,
Russell J. Smith,
Brent Tully,
and Gijs Verdoes Kleijn
[show abstract]
[hide abstract]
ABSTRACT: 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 47, 000 ± 1600 (random) +4000 –5000 (systematic) IGCs out to this radius, and that they make up ~70% of the central GC system, making this the largest GC system in the nearby universe. Even including the GC systems of other cluster galaxies, the IGCs still make up ~30%-45% of the GCs in the cluster core. Observational limits from previous studies of the intracluster light (ICL) suggest that the IGC population has a high specific frequency. If the IGC population has a specific frequency similar to high-SN dwarf galaxies, then the ICL has a mean surface brightness of μ V 27 mag arcsec–2 and a total stellar mass of roughly within the cluster core. The ICL makes up approximately half of the stellar luminosity and one-third of the stellar mass of the central (NGC 4874+ICL) system. The color distribution of the IGC population is bimodal, with blue, metal-poor GCs outnumbering red, metal-rich GCs by a ratio of 4:1. The inner GCs associated with NGC 4874 also have a bimodal distribution in color, but with a redder metal-poor population. The fraction of red IGCs (20%), and the red color of those GCs, implies that IGCs can originate from the halos of relatively massive, L* galaxies, and not solely from the disruption of dwarf galaxies.
The Astrophysical Journal 02/2011; 730(1):23. · 6.02 Impact Factor
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Derek Hammer,
Gijs Verdoes Kleijn,
Carlos Hoyos,
Mark den Brok,
Marc Balcells,
Henry C. Ferguson,
Paul Goudfrooij,
David Carter,
Rafael Guzmán,
Reynier F. Peletier, [......],
Bahram Mobasher,
Mustapha Mouhcine,
Sadanori Okamura,
Sue Percival, Steven Phillipps,
Bianca M. Poggianti,
James Price,
Ray M. Sharples,
R. Brent Tully,
and Edwin Valentijn
[show abstract]
[hide abstract]
ABSTRACT: The Coma cluster, Abell 1656, was the target of an HST-ACS Treasury program designed for deep imaging in the F475W and F814W passbands. Although our survey was interrupted by the ACS instrument failure in early 2007, the partially completed survey still covers ~50% of the core high-density region in Coma. Observations were performed for 25 fields that extend over a wide range of cluster-centric radii (~1.75 Mpc or 1°) with a total coverage area of 274 arcmin2. The majority of the fields are located near the core region of Coma (19/25 pointings) with six additional fields in the southwest region of the cluster. In this paper, we present reprocessed images and SEXTRACTOR source catalogs for our survey fields, including a detailed description of the methodology used for object detection and photometry, the subtraction of bright galaxies to measure faint underlying objects, and the use of simulations to assess the photometric accuracy and completeness of our catalogs. We also use simulations to perform aperture corrections for the SEXTRACTOR Kron magnitudes based only on the measured source flux and its half-light radius. We have performed photometry for ~73,000 unique objects; approximately one-half of our detections are brighter than the 10σ point-source detection limit at F814W = 25.8 mag (AB). The slight majority of objects (60%) are unresolved or only marginally resolved by ACS. We estimate that Coma members are 5%-10% of all source detections, which consist of a large population of unresolved compact sources (primarily globular clusters but also ultra-compact dwarf galaxies) and a wide variety of extended galaxies from a cD galaxy to dwarf low surface brightness galaxies. The red sequence of Coma member galaxies has a color-magnitude relation with a constant slope and dispersion over 9 mag (–21 < M F814W < –13). The initial data release for the HST-ACS Coma Treasury program was made available to the public in 2008 August. The images and catalogs described in this study relate to our second data release.
The Astrophysical Journal Supplement Series 10/2010; 191(1):143. · 13.46 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: As part of the HST/ACS Coma Cluster Treasury Survey, we have undertaken a Keck/LRIS spectroscopic campaign to determine membership for faint dwarf galaxies. In the process, we discovered a population of Ultra Compact Dwarf galaxies (UCDs) in the core region of the Coma cluster. At the distance of Coma, UCDs are expected to have angular sizes 0.01 < R_e < 0.2 arcsec. With ACS imaging, we can resolve all but the smallest ones with careful fitting. Candidate UCDs were chosen based on magnitude, color, and degree of resolution. We spectroscopically confirm 27 objects as bona fide UCD members of the Coma cluster, a 60% success rate for objects targeted with M_R < -12. We attribute the high success rate in part to the high resolution of HST data and to an apparent large population of UCDs in Coma. We find that the UCDs tend to be strongly clustered around giant galaxies, at least in the core region of the cluster, and have a distribution and colors that are similar to globular clusters. These findings suggest that UCDs are not independent galaxies, but rather have a star cluster origin. This current study provides the dense environment datapoint necessary for understanding the UCD population. Comment: 6 pages, 9 figures, to appear in the conference proceedings of "A Universe of Dwarf Galaxies" (Lyon, June 14-18, 2010)
09/2010;
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David T. Hill,
Lee S. Kelvin,
Simon P. Driver,
Aaron S. G. Robotham,
Ewan Cameron,
Nicholas Cross,
Ellen Andrae,
Ivan K. Baldry,
Steven P. Bamford,
Joss Bland-Hawthorn, [......], Steven Phillipps,
Kevin A. Pimbblet,
Cristina C. Popescu,
Matthew Prescott,
Mark Seibert,
Rob G. Sharp,
Will J. Sutherland,
Daniel Thomas,
Richard J. Tuffs,
Elco van Kampen
[show abstract]
[hide abstract]
ABSTRACT: In order to generate credible 0.1-2 {\mu}m SEDs, the GAMA project requires many Gigabytes of imaging data from a number of instruments to be re-processed into a standard format. In this paper we discuss the software infrastructure we use, and create self-consistent ugrizYJHK photometry for all sources within the GAMA sample. Using UKIDSS and SDSS archive data, we outline the pre-processing necessary to standardise all images to a common zeropoint, the steps taken to correct for seeing bias across the dataset, and the creation of Gigapixel-scale mosaics of the three 4x12 deg GAMA regions in each filter. From these mosaics, we extract source catalogues for the GAMA regions using elliptical Kron and Petrosian matched apertures. We also calculate S\'ersic magnitudes for all galaxies within the GAMA sample using SIGMA, a galaxy component modelling wrapper for GALFIT 3. We compare the resultant photometry directly, and also calculate the r band galaxy LF for all photometric datasets to highlight the uncertainty introduced by the photometric method. We find that (1) Changing the object detection threshold has a minor effect on the best-fitting Schechter parameters of the overall population (M* +/- 0.055mag, {\alpha} +/- 0.014, {\Phi}* +/- 0.0005 h^3 Mpc^{-3}). (2) An offset between datasets that use Kron or Petrosian photometry regardless of the filter. (3) The decision to use circular or elliptical apertures causes an offset in M* of 0.20mag. (4) The best-fitting Schechter parameters from total-magnitude photometric systems (such as SDSS modelmag or S\'ersic magnitudes) have a steeper faint-end slope than photometry dependent on Kron or Petrosian magnitudes. (5) Our Universe's total luminosity density, when calculated using Kron or Petrosian r-band photometry, is underestimated by at least 15%. Comment: 38 pages, 10 Tables, 26 figures. Submitted to MNRAS (revised once). Image resolution has been lowered. For higher resolution, see http://www.gama-survey.org/
09/2010;
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[show abstract]
[hide abstract]
ABSTRACT: We explore the shape of the galaxy luminosity function (LF) in groups of different mass by creating composite LFs over large numbers of groups. Following previous work using total group luminosity as the mass indicator, here we split our groups by multiplicity and by estimated virial (group halo) mass, and consider red (passive) and blue (star-forming) galaxies separately. In addition, we utilize two different group catalogues (2PIGG and Yang et al.) in order to ascertain the impact of the specific grouping algorithm and further investigate the environmental effects via variations in the LF with position in groups. Our main results are that LFs show a steepening faint end for early-type galaxies as a function of group mass/multiplicity, with a much suppressed trend (evident only in high mass groups) for late-type galaxies. Variations between LFs as a function of group mass are robust irrespective of which grouping catalogue is used, and broadly speaking what method for determining group ‘mass’ is used. We find in particular that there is a significant deficit of low-mass passive galaxies in low-multiplicity groups, as seen in high-redshift clusters. Further to this, the variation in the LF appears to only occur in the central regions of systems, and in fact seems to be most strongly dependent on the position in the group relative to the virial radius. Finally, distance–rank magnitude relations were considered. Only the Yang groups demonstrated any evidence of a correlation between a galaxy's position relative to the brightest group member and its luminosity. 2PIGG possessed no such gradient, the conclusion being the friend-of-friend algorithm suppresses the signal for weak luminosity–position trends and the Yang grouping algorithm naturally enhances it.
Monthly Notices of the Royal Astronomical Society 04/2010; 403(4):1812 - 1828. · 4.90 Impact Factor
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Simon P. Driver,
Peder Norberg,
Ivan K. Baldry,
Steven P. Bamford,
Andrew M. Hopkins,
Jochen Liske,
Jon Loveday,
John A. Peacock,
David T. Hill,
Lee S. Kelvin, [......],
Barry F. Madore,
Mark Seibert,
Martin J. Meyer,
Lister Staveley-Smith, Steven Phillipps,
Cristina C. Popescu,
Ann E. Sansom,
Will J. Sutherland,
Richard J. Tuffs,
Steven J. Warren
[show abstract]
[hide abstract]
ABSTRACT: The Galaxy And Mass Assembly (GAMA) project is the latest in a tradition of large galaxy redshift surveys, and is now underway on the 3.9m Anglo-Australian Telescope at Siding Spring Observatory. GAMA is designed to map extragalactic structures on scales of 1kpc - 1Mpc in complete detail to a redshift of z~0.2, and to trace the distribution of luminous galaxies out to z~0.5. The principal science aim is to test the standard hierarchical structure formation paradigm of Cold Dark Matter (CDM) on scales of galaxy groups, pairs, discs, bulges and bars. We will measure (1) the Dark Matter Halo Mass Function (as inferred from galaxy group velocity dispersions); (2) baryonic processes, such as star formation and galaxy formation efficiency (as derived from Galaxy Stellar Mass Functions); and (3) the evolution of galaxy merger rates (via galaxy close pairs and galaxy asymmetries). Additionally, GAMA will form the central part of a new galaxy database, which aims to contain 275,000 galaxies with multi-wavelength coverage from coordinated observations with the latest international ground- and space-based facilities: GALEX, VST, VISTA, WISE, HERSCHEL, GMRT and ASKAP. Together, these data will provide increased depth (over 2 magnitudes), doubled spatial resolution (0.7"), and significantly extended wavelength coverage (UV through Far-IR to radio) over the main SDSS spectroscopic survey for five regions, each of around 50 deg^2. This database will permit detailed investigations of the structural, chemical, and dynamical properties of all galaxy types, across all environments, and over a 5 billion year timeline. Comment: GAMA overview which appeared in the October 2009 issue of Astronomy & Geophysics, ref: Astron.Geophys. 50 (2009) 5.12
10/2009;
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[show abstract]
[hide abstract]
ABSTRACT: We describe a sample of 13 bright (18.5 < BJ < 20.1), compact galaxies at low redshift (0.05 < z < 0.21) behind the Fornax Cluster. These galaxies are unresolved on UK Schmidt sky survey plates, and so they would be missing from most galaxy catalogs compiled from this material. The objects were found during initial observations of The Fornax Spectroscopic Survey. This project is using the Two-degree Field spectrograph on the Anglo-Australian Telescope to obtain spectra for a complete sample of all 14,000 objects, stellar and nonstellar, with 16.5 < BJ < 19.7, in a 12 deg2 area centered on the Fornax Cluster of galaxies. The surface density of compact galaxies with magnitudes 16.5 < BJ < 19.7 is 7 ± 3 deg-2, representing 2.8% ± 1.6% of all local (z < 0.2) galaxies to this limit. There are 12 ± 3 deg-2 with 16.5 < BJ < 20.2. They are luminous (-21.5 < MB < -18.0, for H0 = 50 km s-1 Mpc-1), and most have strong emission lines (Hα equivalent widths of 40-200 Å) and small sizes typical of luminous H II galaxies and compact narrow emission line galaxies. Four out of 13 have red colors and early-type spectra, and so they are unlikely to have been detected in any previous surveys.
The Astrophysical Journal 12/2008; 511(2):L97. · 6.02 Impact Factor
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The Astronomical Journal 12/2008; · 4.03 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We derive composite luminosity functions (LF) for galaxies in groups and examine the behavior of the LF as a function of group luminosity (used as an indicator of group or halo mass). We consider both the entire galaxy population and galaxies split into red and blue (quiescent and star-forming) samples, in order to examine possible mechanisms behind observed variations of galaxy properties with environment. We find evidence that M* brightens and α steepens with group luminosity, until a threshold value where the LF parameters stabilize at those found in rich clusters. The effect is seen in the total LF and for the blue and red galaxies separately. The behavior of the quiescent and star-forming samples is qualitatively consistent with variations resulting from interactions and mergers, where mergers build the bright end of the luminosity function at the same time as dwarf irregulars have their star formation quenched and evolve into dwarf ellipticals. These processes appear to take place preferentially in low-luminosity groups and to be complete at a group luminosity of -22.5 in B, corresponding to a halo mass of order 1013.5 ☉.
The Astrophysical Journal 12/2008; 652(2):1077. · 6.02 Impact Factor
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David Carter,
Paul Goudfrooij,
Bahram Mobasher,
Henry C. Ferguson,
Thomas H. Puzia,
Alfonso L. Aguerri,
Marc Balcells,
Dan Batcheldor,
Terry J. Bridges,
Jonathan I. Davies, [......],
Sadanori Okamura,
Reynier F. Peletier, Steven Phillipps,
Bianca M. Poggianti,
Ray M. Sharples,
Russell J. Smith,
Neil Trentham,
R. Brent Tully,
Edwin Valentijn,
and Gijs Verdoes Kleijn
[show abstract]
[hide abstract]
ABSTRACT: We describe the HST ACS Coma Cluster Treasury survey, a deep two-passband imaging survey of one of the nearest rich clusters of galaxies, the Coma Cluster (Abell 1656). The survey was designed to cover an area of 740 arcmin2 in regions of different density of both galaxies and intergalactic medium within the cluster. The ACS failure of 2007 January 27 leaves the survey 28% complete, with 21 ACS pointings (230 arcmin2) complete, and partial data for a further four pointings (44 arcmin2). The predicted survey depth for 10 σ detections for optimal photometry of point sources is g' = 27.6 in the F475W filter and IC = 26.8 mag in F814 (AB magnitudes). Initial simulations with artificially injected point sources show 90% recovered at magnitude limits of g' = 27.55 and IC = 26.65. For extended sources, the predicted 10 σ limits for a 1 arcsec2 region are g' = 25.8 mag arcsec−2 and IC = 25.0 mag arcsec−2. We highlight several motivating science goals of the survey, including study of the faint end of the cluster galaxy luminosity function, structural parameters of dwarf galaxies, stellar populations and their effect on colors and color gradients, evolution of morphological components in a dense environment, the nature of ultracompact dwarf galaxies, and globular cluster populations of cluster galaxies of a range of luminosities and types. This survey will also provide a local rich cluster benchmark for various well-known global scaling relations and explore new relations pertaining to the nuclear properties of galaxies.
The Astrophysical Journal Supplement Series 12/2008; 176(2):424. · 13.46 Impact Factor
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David Carter,
Paul Goudfrooij,
Bahram Mobasher,
Henry C. Ferguson,
Thomas H. Puzia,
Alfonso L. Aguerri,
Marc Balcells,
Dan Batcheldor,
Terry J. Bridges,
Jonathan I. Davies, [......],
Sadanori Okamura,
Reynier F. Peletier, Steven Phillipps,
Bianca M. Poggianti,
Ray M. Sharples,
Russell J. Smith,
Neil Trentham,
R. Brent Tully,
Edwin Valentijn,
Gijs Verdoes Kleijn
[show abstract]
[hide abstract]
ABSTRACT: We describe the HST ACS Coma cluster Treasury survey, a deep two-passband imaging survey of one of the nearest rich clusters of galaxies, the Coma cluster (Abell 1656). The survey was designed to cover an area of 740 square arcmin in regions of different density of both galaxies and intergalactic medium within the cluster. The ACS failure of January 27th 2007 leaves the survey 28% complete, with 21 ACS pointings (230 square arcmin) complete, and partial data for a further 4 pointings (44 square arcmin). Predicted survey depth for 10 sigma detections for optimal photometry of point sources is g' = 27.6 in the F475W filter, and IC=26.8 mag in F814 (AB magnitudes). Initial simulations with artificially injected point sources show 90% recovered at magnitude limits of g' = 27.55 and IC = 26.65. For extended sources, the predicted 10 sigma limits for a 1 square arcsecond region are g' = 25.8 mag/sq. arcsec and IC = 25.0 mag/sq. arcsec. We highlight several motivating science goals of the survey, including study of the faint end of the cluster galaxy luminosity function, structural parameters of dwarf galaxies, stellar populations and their effect on colors and color gradients, evolution of morphological components in a dense environment, the nature of ultra compact dwarf galaxies, and globular cluster populations of cluster galaxies of a range of luminosities and types. This survey will also provide a local rich cluster benchmark for various well known global scaling relations and explore new relations pertaining to the nuclear properties of galaxies.
02/2008;
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[show abstract]
[hide abstract]
ABSTRACT: We derive probability density functions for the projected axial ratios of the real and mock 2PIGG galaxy groups, and use this data to investigate the intrinsic three dimensional shape of the dark matter ellipsoids that they trace. As well as analysing the raw data for groups of varying multiplicities, a convolution corrected form of the data is also considered which weights the probability density function according to the results of multiple Monte-Carlo realizations of discrete samples from the input spatial distributions. The important effect observed is that the best fit distribution for all the raw data is a prolate ellipsoid with a Gaussian distribution of axial ratios with ¯ β = 0.36 and σ = 0.14, whilst for the convolved data the best fit solution is that of an oblate ellipsoid ¯ β = 0.22 and σ = 0.1. Previously only prolate distributions were thought compatible with the data, this being interprated as evidence of filamentary collapse at nodes. We also find that even after allowing for the sampling effects, the corrected data is better fit using separate multiplicity bins, which display a trend towards more spherical halos in higher multiplicity groups. Finally, we find that all results in the real data are in good agreement with the mock data from ΛCDM simulations, KS tests showing that all comparative data have been drawn from the same distributions within the 1σ confidence limits.
11/2007;
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ABSTRACT: We derive composite luminosity functions (LF) for galaxies in groups and examine the behaviour of the LF as a function of group luminosity (used as an indicator of group or halo mass). We consider both the entire galaxy population and split galaxies into red and blue (quiescent and star forming) samples, in order to examine possible mechanisms behind observed variations of galaxy properties with environment. We find evidence that $M^*$ brightens and $\alpha$ steepens with group luminosity, until a threshold value where the LF parameters stabilize at those found in rich clusters. The effect is seen in the total LF and for the blue and red galaxies separately. The behaviour of the quiescent and star-forming samples is qualitatively consistent with variations resulting from interactions and mergers, where mergers build the bright end of the luminosity function at the same time as dwarf irregulars have their star formation quenched and evolve into dwarf ellipticals. These processes appear to take place preferentially in low luminosity groups and to be complete at a group luminosity of -22.5 in $B$, corresponding to a halo mass of order $10^{13.5} M_{\odot}$. Comment: Accepted by ApJ
08/2006;
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ABSTRACT: Using 10 095 galaxies (B < 20 mag) from the Millennium Galaxy Catalogue, we
derive B-band luminosity distributions and selected bivariate brightness
distributions for the galaxy population. All subdivisions extract highly
correlated sub-sets of the galaxy population which consistently point towards
two overlapping distributions. A clear bimodality in the observed distribution
is seen in both the rest-(u-r) colour and log(n) distributions. The rest-(u-r)
colour bimodality becomes more pronounced when using the core colour as opposed
to global colour. The two populations are extremely well separated in the
colour-log(n) plane. Using our sample of 3 314 (B < 19 mag) eyeball classified
galaxies, we show that the bulge-dominated, early-type galaxies populate one
peak and the bulge-less, late-type galaxies occupy the second. The early- and
mid-type spirals sprawl across and between the peaks. This constitutes
extremely strong evidence that the fundamental way to divide the luminous
galaxy population is into bulges and discs and that the galaxy bimodality
reflects the two component nature of galaxies and not two distinct galaxy
classes. We argue that these two-components require two independent formation
mechanisms/processes and advocate early bulge formation through initial
collapse and ongoing disc formation through splashback, infall and
merging/accretion. We calculate the B-band luminosity-densities and
stellar-mass densities within each subdivision and estimate that the z ~ 0
stellar mass content in spheroids, bulges and discs is 35 +/- 2 per cent, 18
+/- 7 and 47 +/- 7 per cent respectively. [Abridged]
02/2006;
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ABSTRACT: We report on the morphological luminosity functions (LFs) and radial profiles derived for the galaxy population within the rich cluster Abell 868 (z=0.153) based purely on Hubble Space Telescope Imaging in F606W. We recover Schechter functions for early(E/S0)-, mid(Sabc)- and late(Sd/Irr)- type galaxies. The early-, mid- and late- types are all consistent with the recent field morphological LFs based on recent analysis of the Sloan Digital Sky Survey -- Early Data Release (SDSS-EDR; Nakamura et al 2003). From a detailed error analysis, including clustering of the background population, we note that improved statistics can only come from combining data from many clusters. We also examine the luminosity-density and number-density profiles as a function of morphology and draw the following conclusions: (1) The galaxies responsible for the steep faint-end slope are predominantly of late-type morphology, (2) The cluster core is dominated by elliptical galaxies, (3) The core is devoid of late-types systems, (4) The luminosity-density as a function of morphological type is skewed towards early-types when compared to the field, (5) Up to half of the elliptical galaxies may have formed from the spiral population through core disk-destruction process(es). We believe the most plausible explanation is the conventional one that late-types are destroyed during transit through the cluster core and that mid-types are converted into early-types through a similar process, which destroys the outer disk and results in a more tightly bound population of core ellipticals.[Abridged]. Comment: Accepted for publication in The Astronomical Journal (December issue). Figures 1, 2 and 5 degraded to adhere to astro-ph byte limit
09/2003;
