-
Boris Häußler,
Steven P. Bamford,
Marina Vika,
Alex L. Rojas,
Marco Barden,
Lee S. Kelvin,
Mehmet Alpaslan,
Aaron S. G. Robotham,
Simon P. Driver,
I. K. Baldry,
Sarah Brough, Andrew M. Hopkins,
Jochen Liske,
Robert C. Nichol,
Cristina. C. Popescu,
Richard J. Tuffs
[show abstract]
[hide abstract]
ABSTRACT: In this paper, we demonstrate a new method for fitting galaxy profiles which
makes use of the full multi-wavelength data provided by modern large
optical-near-infrared imaging surveys. We present a new version of GALAPAGOS,
which utilises a recently-developed multi-wavelength version of GALFIT, and
enables the automated measurement of wavelength dependent S\'ersic profile
parameters for very large samples of galaxies. Our new technique is extensively
tested to assess the reliability of both pieces of software, GALFIT and
GALAPAGOS on both real ugrizY JHK imaging data from the GAMA survey and
simulated data made to the same specifications. We find that fitting galaxy
light profiles with multi-wavelength data increases the stability and accuracy
of the measured parameters, and hence produces more complete and meaningful
multi-wavelength photometry than has been available previously. The improvement
is particularly significant for magnitudes in low S/N bands and for structural
parameters like half-light radius re and S\'ersic index n for which a prior is
used by constraining these parameters to a polynomial as a function of
wavelength. This allows the fitting routines to push the magnitude of galaxies
for which sensible values can be derived to fainter limits. The technique
utilises a smooth transition of galaxy parameters with wavelength, creating
more physically meaningful transitions than single-band fitting and allows
accurate interpolation between passbands, perfect for derivation of rest-frame
values.
12/2012;
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Lisa M. R. Fogarty,
Joss Bland-Hawthorn,
Scott M. Croom,
Andrew W. Green,
Julia J. Bryant,
Jon S. Lawrence,
Samuel Richards,
James T. Allen,
Amanda E. Bauer,
Michael N. Birchall, [......],
Geraint Lewis,
Ángel R. López-Sánchez,
Stan Miziarski,
Holly Trowland,
Sergio G. Leon-Saval,
Seong-Sik Min,
Christopher Trinh,
Gerald Cecil,
Sylvain Veilleux,
Kory Kreimeyer
[show abstract]
[hide abstract]
ABSTRACT: We present the first scientific results from the Sydney-AAO Multi-Object IFS
(SAMI) at the Anglo-Australian Telescope. This unique instrument deploys 13
fused fibre bundles (hexabundles) across a one-degree field of view allowing
simultaneous spatially-resolved spectroscopy of 13 galaxies. During the first
SAMI commissioning run, targeting a single galaxy field, one object (ESO
185-G031) was found to have extended minor axis emission with ionisation and
kinematic properties consistent with a large-scale galactic wind. The
importance of this result is two-fold: (i) fibre bundle spectrographs are able
to identify low-surface brightness emission arising from extranuclear activity;
(ii) such activity may be more common than presently assumed because
conventional multi-object spectrographs use single-aperture fibres and spectra
from these are nearly always dominated by nuclear emission. These early results
demonstrate the extraordinary potential of multi-object hexabundle spectroscopy
in future galaxy surveys.
The Astrophysical Journal 12/2012; 761(2):169. · 6.02 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: [Abridged] It is widely accepted that observations at mid-infrared (mid-IR)
wavelengths enable the selection of galaxies with nuclear activity, which may
not be revealed even in the deepest X-ray surveys. In this work new near- and
mid-IR color diagnostics are explored, aiming for improved efficiency - better
completeness and less contamination - in selecting AGN out to very high
redshifts. We restrict our study to the James Webb Space Telescope wavelength
range (0.6-27um). The criteria are created based on the predictions by
state-of-the-art galaxy and AGN templates covering a wide variety of galaxy
properties, and tested against control samples with deep multi-wavelength
coverage (ranging from the X-rays to radio frequencies). We show that the
colors Ks-[4.5], [4.5]-[8.0], and [8.0]-[24] are ideal as AGN/non-AGN
diagnostics at, respectively, z<~1, 1<~z<~2.5, and z>~2.5-3. However, when the
source redshift is unknown, these colors should be combined. We thus develop an
improved IR criterion (using Ks and IRAC bands, KI) as a new alternative at
z<~2.5. KI does not show improved completeness (50-60% overall) in comparison
to commonly used IRAC-based AGN criteria, but is less affected by non-AGN
contamination (revealing a >50-90% level of successful AGN selection). We also
propose KIM (using Ks, IRAC, and MIPS-24um bands, KIM), which aims to select
AGN hosts from local distances to as far back as the end of reionization
(0<z<~7) with reduced non-AGN contamination. However, the necessary
testing-constraints and the small control-sample sizes prevent the confirmation
of its improved efficiency at z<~2.5. Overall, KIM shows a ~30-40% completeness
and a >70-90% level of successful AGN selection. KI and KIM are built to be
reliable against a ~10-20% error in flux, are based on existing filters, and
are suitable for immediate use.
05/2012;
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Mehmet Alpaslan,
Aaron S. G. Robotham,
Simon Driver,
Peder Norberg,
John A. Peacock,
Ivan Baldry,
Joss Bland-Hawthorn,
Sarah Brough, Andrew M. Hopkins,
Lee S. Kelvin,
Jochen Liske,
Jon Loveday,
Alexander Merson,
Robert C. Nichol,
Kevin Pimbblet
[show abstract]
[hide abstract]
ABSTRACT: We have generated complementary halo mass estimates for all groups in the
Galaxy And Mass Assembly Galaxy Group Catalogue (GAMA G3Cv1) using a modified
caustic mass estimation algorithm, originally developed by Diaferio & Geller
(1997). We calibrate the algorithm by applying it on a series of 9 GAMA mock
galaxy light cones and investigate the effects of using different definitions
for group centre and size. We select the set of parameters that provide
median-unbiased mass estimates when tested on mocks, and generate mass
estimates for the real group catalogue. We find that on average, the caustic
mass estimates agree with dynamical mass estimates within a factor of 2 in 90.8
+/- 6.1% groups and compares equally well to velocity dispersion based mass
estimates for both high and low multiplicity groups over the full range of
masses probed by the G3Cv1.
04/2012;
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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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Scott M. Croom,
Jon S. Lawrence,
Joss Bland-Hawthorn,
Julia J. Bryant,
Lisa Fogarty,
Samuel Richards,
Michael Goodwin,
Tony Farrell,
Stan Miziarski,
Ron Heald, [......],
Amanda E. Bauer,
Michael N. Birchall,
Simon Ellis,
Anthony Horton,
Sergio Leon-Saval,
Geraint Lewis,
A. R. Lopez-Sanchez,
Seong-Sik Min,
Christopher Trinh,
Holly Trowland
[show abstract]
[hide abstract]
ABSTRACT: We demonstrate a novel technology that combines the power of the multi-object
spectrograph with the spatial multiplex advantage of an integral field
spectrograph (IFS). The Sydney-AAO Multi-object IFS (SAMI) is a prototype
wide-field system at the Anglo-Australian Telescope (AAT) that allows 13
imaging fibre bundles ("hexabundles") to be deployed over a 1-degree diameter
field of view. Each hexabundle comprises 61 lightly-fused multimode fibres with
reduced cladding and yields a 75 percent filling factor. Each fibre core
diameter subtends 1.6 arcseconds on the sky and each hexabundle has a field of
view of 15 arcseconds diameter. The fibres are fed to the flexible AAOmega
double-beam spectrograph, which can be used at a range of spectral resolutions
(R=lambda/delta(lambda) ~ 1700-13000) over the optical spectrum (3700-9500A).
We present the first spectroscopic results obtained with SAMI for a sample of
galaxies at z~0.05. We discuss the prospects of implementing hexabundles at a
much higher multiplex over wider fields of view in order to carry out
spatially--resolved spectroscopic surveys of 10^4 to 10^5 galaxies.
Monthly Notices of the Royal Astronomical Society 03/2012; 421(1):872. · 4.90 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We have developed a multiscale structure identification algorithm for the
detection of overdensities in galaxy data that identifies structures having
radii within a user-defined range. Our "multiscale probability mapping"
technique combines density estimation with a shape statistic to identify local
peaks in the density field. This technique takes advantage of a user-defined
range of scale sizes, which are used in constructing a coarse-grained map of
the underlying fine-grained galaxy distribution, from which overdense
structures are then identified. In this study we have compiled a catalogue of
groups and clusters at 0.025 < z < 0.24 based on the Sloan Digital Sky Survey,
Data Release 7, quantifying their significance and comparing with other
catalogues. Most measured velocity dispersions for these structures lie between
50 and 400 km/s. A clear trend of increasing velocity dispersion with radius
from 0.2 to 1 Mpc/h is detected, confirming the lack of a sharp division
between groups and clusters. A method for quantifying elongation is also
developed to measure the elongation of group and cluster environments. By using
our group and cluster catalogue as a coarse-grained representation of the
galaxy distribution for structure sizes of <~ 1 Mpc/h, we identify 53 filaments
(from an algorithmically-derived set of 100 candidates) as elongated unions of
groups and clusters at 0.025 < z < 0.13. These filaments have morphologies that
are consistent with previous samples studied.
01/2012;
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[show abstract]
[hide abstract]
ABSTRACT: We perform a pixel-by-pixel analysis of 467 galaxies in the GOODS-VIMOS
survey to study systematic effects in extracting properties of stellar
populations (age, dust, metallicity and SFR) from pixel colors using the
pixel-z method. The systematics studied include the effect of the input stellar
population synthesis model, passband limitations and differences between
individual SED fits to pixels and global SED-fitting to a galaxy's colors. We
find that with optical-only colors, the systematic errors due to differences
among the models are well constrained. The largest impact on the age and SFR
e-folding time estimates in the pixels arises from differences between the
Maraston models and the Bruzual&Charlot models, when optical colors are used.
This results in systematic differences larger than the 2{\sigma} uncertainties
in over 10 percent of all pixels in the galaxy sample. The effect of
restricting the available passbands is more severe. In 26 percent of pixels in
the full sample, passband limitations result in systematic biases in the age
estimates which are larger than the 2{\sigma} uncertainties. Systematic effects
from model differences are reexamined using Near-IR colors for a subsample of
46 galaxies in the GOODS-NICMOS survey. For z > 1, the observed optical/NIR
colors span the rest frame UV-optical SED, and the use of different models does
not significantly bias the estimates of the stellar population parameters
compared to using optical-only colors. We then illustrate how pixel-z can be
applied robustly to make detailed studies of substructure in high redshift
galaxies such as (a) radial gradients of age, SFR, sSFR and dust and (b) the
distribution of these properties within subcomponents such as spiral arms and
clumps. Finally, we show preliminary results from the CANDELS survey
illustrating how the new HST/WFC3 data can be exploited to probe substructure
in z~1-3 galaxies.
12/2011;
-
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;
-
Edward N. Taylor, Andrew M. Hopkins,
Ivan K. Baldry,
Michael J I Brown,
Simon P. Driver,
Lee S. Kelvin,
David T. Hill,
Aaron S. G. Robotham,
Joss Bland-Hawthorn,
D. H. Jones, [......],
R. C. Nichol,
H. R. Parkinson,
S. Phillipps,
K. A. Pimbblet,
C. C. Popescu,
Matthew Prescott,
W. J. Sutherland,
R. J. Tuffs,
Eelco van Kampen,
D. Wijesinghe
[show abstract]
[hide abstract]
ABSTRACT: This paper describes the first catalogue of photometrically-derived stellar
mass estimates for intermediate-redshift (z < 0.65) galaxies in the Galaxy And
Mass Assembly (GAMA) spectroscopic redshift survey. These masses, as well as
the full set of ancillary stellar population parameters, will be made public as
part of GAMA data release 2. Although the GAMA database does include NIR
photometry, we show that the quality of our stellar population synthesis fits
is significantly poorer when these NIR data are included. Further, for a large
fraction of galaxies, the stellar population parameters inferred from the
optical-plus-NIR photometry are formally inconsistent with those inferred from
the optical data alone. This may indicate problems in our stellar population
library, or NIR data issues, or both; these issues will be addressed for future
versions of the catalogue. For now, we have chosen to base our stellar mass
estimates on optical photometry only. In light of our decision to ignore the
available NIR data, we examine how well stellar mass can be constrained based
on optical data alone. We use generic properties of stellar population
synthesis models to demonstrate that restframe colour alone is in principle a
very good estimator of stellar mass-to-light ratio, M*/Li. Further, we use the
observed relation between restframe (g-i) and M*/Li for real GAMA galaxies to
argue that, modulo uncertainties in the stellar evolution models themselves,
(g-i) colour can in practice be used to estimate M*/Li to an accuracy of < ~0.1
dex. This 'empirically calibrated' (g-i)-M*/Li relation offers a simple and
transparent means for estimating galaxies' stellar masses based on minimal
data, and so provides a solid basis for other surveys to compare their results
to z < ~0.4 measurements from GAMA.
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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Dinuka B. Wijesinghe,
Elisabete da Cunha, Andrew M. Hopkins,
Loretta Dunne,
R. Sharp,
M. Gunawardhana,
S. Brough,
E. M. Sadler,
S. Driver,
I. Baldry, [......],
A. S. G. Robotham,
E. E. Rigby,
M. Seibert,
S. Serjeant,
D. J. B. Smith,
P. Temi,
W. Sutherland,
E. Taylor,
D Thomas,
P. van der Werf
[show abstract]
[hide abstract]
ABSTRACT: We use multiwavelength data from the Galaxy And Mass Assembly (GAMA) and
Herschel ATLAS (H-ATLAS) surveys to compare the relationship between various
dust obscuration measures in galaxies. We explore the connections between the
ultraviolet (UV) spectral slope, $\beta$, the Balmer decrement, and the far
infrared (IR) to $150\,$nm far ultraviolet (FUV) luminosity ratio. We explore
trends with galaxy mass, star formation rate (SFR) and redshift in order to
identify possible systematics in these various measures. We reiterate the
finding of other authors that there is a large scatter between the Balmer
decrement and the $\beta$ parameter, and that $\beta$ may be poorly constrained
when derived from only two broad passbands in the UV. We also emphasise that
FUV derived SFRs, corrected for dust obscuration using $\beta$, will be
overestimated unless a modified relation between $\beta$ and the attenuation
factor is used. Even in the optimum case, the resulting SFRs have a significant
scatter, well over an order of magnitude. While there is a stronger correlation
between the IR to FUV luminosity ratio and $\beta$ parameter than with the
Balmer decrement, neither of these correlations are particularly tight, and
dust corrections based on $\beta$ for high redshift galaxy SFRs must be treated
with caution. We conclude with a description of the extent to which the
different obscuration measures are consistent with each other as well as the
effects of including other galactic properties on these correlations.
Monthly Notices of the Royal Astronomical Society 03/2011; 415(2). · 4.90 Impact Factor
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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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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: In this second of a series of papers on spatially resolved star formation, we investigate the impact of the density-morphology relation of galaxies on the spatial variation of star formation (SF) and its dependence on environment. We find that while a density-morphology relation is present for the sample, it cannot solely explain the observed suppression of SF in galaxies in high-density environments. We also find that early-type and late-type galaxies exhibit distinct radial star formation rate (SFR) distributions, with early-types having a SFR distribution that extends further relative to the galaxy scale length, compared to late-types at all densities. We find that a suppression of SF in the highest density environments is found in the highest star forming galaxies for both galaxy types. This suppression occurs in the innermost regions in late-types (r <= 0.125 Petrosian radii), and further out in radius in early-types (0.125< r <= 0.25 Petrosian radii). When the full sample is considered no clear suppression of SF is detected, indicating that the environmental trends are driven only by the highest SF galaxies. We demonstrate that the density-morphology relation alone cannot account for the suppression of SF in the highest density environments. This points to an environmentally-governed evolutionary mechanism that affects the SF in the innermost regions in both early and late-type galaxies. We suggest that this is a natural consequence of the "downsizing" of SF in galaxies. Comment: 31 pages, 8 figures, replaced with accepted version, added references
01/2009;
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[show abstract]
[hide abstract]
ABSTRACT: We present the results of a study of a sample of 375 extremely red galaxies (ERGs) in the Phoenix Deep Survey, 273 of which constitute a subsample which is 80% complete to Ks = 18.5 over an area of 1160 arcmin2. The angular correlation function for ERGs is estimated, and the association of ERGs with faint radio sources explored. We find tentative evidence that ERGs and faint radio sources are associated at z 0.5. A new overdensity-mapping algorithm has been used to characterize the ERG distribution, and identify a number of cluster candidates, including a likely cluster containing ERGs at 0.5 < z < 1. Our algorithm is also used in an attempt to probe the environments in which faint radio sources and ERGs are associated. We find limited evidence that the I – Ks > 4 criterion is more efficient than R – Ks > 5 at selecting dusty star-forming galaxies, rather than passively evolving ERGs.
The Astronomical Journal 06/2008; 136(1):358. · 4.03 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We use the photometric information contained in individual pixels of 44,964 (0.019<z<0.125 and -23.5<M_r<-20.5) galaxies in the Fourth Data Release (DR4) of the Sloan Digital Sky Survey to investigate the effects of environment on galaxy star formation (SF). We use the pixel-z technique, which combines stellar population synthesis models with photometric redshift template fitting on the scale of individual pixels in galaxy images. Spectral energy distributions are constructed, sampling a wide range of properties such as age, star formation rate (SFR), dust obscuration and metallicity. By summing the SFRs in the pixels, we demonstrate that the distribution of total galaxy SFR shifts to lower values as the local density of surrounding galaxies increases, as found in other studies. The effect is most prominent in the galaxies with the highest star formation, and we see the break in the SFR-density relation at a local galaxy density of $\approx 0.05 $(Mpc/h)$^{-3}$. Since our method allows us to spatially resolve the SF distribution within galaxies, we can calculate the mean SFR of each galaxy as a function of radius. We find that on average the mean SFR is dominated by SF in the central regions of galaxies, and that the trend for suppression of SFR in high density environments is driven by a reduction in this nuclear SF. We also find that the mean SFR in the outskirts is largely independent of environmental effects. This trend in the mean SFR is shared by galaxies which are highly star forming, while those which are weakly star forming show no statistically significant correlation between their environment and the mean SFR at any radius. Comment: 37 pages, 11 figures. Referee's comments included and matches version accepted for publication in the Astrophysical Journal. For high resolution figures, see http://www.phyast.pitt.edu/~welikala/pixelz/paper1/
11/2007;
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Elaine M. Sadler,
Russell D. Cannon,
Tom Mauch,
Paul J. Hancock,
David A. Wake,
Nic Ross,
Scott M. Croom,
Michael J. Drinkwater,
Alastair C. Edge,
Daniel Eisenstein, Andrew M. Hopkins,
Helen Johnston,
Robert Nichol,
Kevin A. Pimbblet,
Roberto De Propris,
Isaac G. Roseboom,
Donald P. Schneider,
Tom Shanks
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ABSTRACT: We have combined optical data from the 2dF-SDSS Luminous Red Galaxy and QSO (2SLAQ) redshift survey with radio measurements from the 1.4 GHz VLA FIRST and NVSS surveys to identify a volume-limited sample of 391 radio galaxies at redshift 0.4<z<0.7. By determining an accurate radio luminosity function for early-type galaxies in this redshift range, we can investigate the cosmic evolution of the radio-galaxy population over a wide range in radio luminosity. The low-power radio galaxies in our LRG sample (those with 1.4 GHz radio luminosities in the range 10^{24} to 10^{25} W/Hz, corresponding to FR I radio galaxies in the local universe) undergo significant cosmic evolution over the redshift range 0<z<0.7, consistent with pure luminosity evolution of the form (1+z)^k where k=2.0+/-0.3. Our results appear to rule out (at the 6-7 sigma level) models in which low-power radio galaxies undergo no cosmic evolution. The most powerful radio galaxies in our sample (with radio luminosities above 10^{26} W/Hz) may undergo more rapid evolution over the same redshift range. The evolution seen in the low-power radio-galaxy population implies that the total energy input into massive early-type galaxies from AGN heating increases with redshift, and was roughly 50% higher at z~0.55 (the median redshift of the 2SLAQ LRG sample) than in the local universe. Comment: 18 pages, 15 figures, one 10-page data table in landscape format. Replaced with final version accepted for publication in MNRAS
12/2006;
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ABSTRACT: We analyze the photometric information contained in individual pixels of galaxies in the Hubble Deep Field North (HDFN) using a new technique, _pixel-z_, that combines predictions of evolutionary synthesis models with photometric redshift template fitting. Each spectral energy distribution template is a result of modeling of the detailed physical processes affecting gas properties and star formation efficiency. The criteria chosen to generate the SED templates is that of sampling a wide range of physical characteristics such as age, star formation rate, obscuration and metallicity. A key feature of our method is the sophisticated use of error analysis to generate error maps that define the reliability of the template fitting on pixel scales and allow for the separation of the interplay among dust, metallicity and star formation histories. This technique offers a number of advantages over traditional integrated color studies. As a first application, we derive the star formation and metallicity histories of galaxies in the HDFN. Our results show that the comoving density of star formation rate, determined from the UV luminosity density of sources in the HDFN, increases monotonically with redshift out to at least redshift of 5. This behavior can plausibly be explained by a smooth increase of the UV luminosity density with redshift coupled with an increase in the number of star forming regions as a function of redshift. We also find that the information contained in individual pixels in a galaxy can be linked to its morphological history. Finally, we derive the metal enrichment rate history of the universe and find it in good agreement with predictions based on the evolving HI content of Lyman-alpha QSO absorption line systems. Comment: Accepted for publication in the Astronomical Journal. Full resolution figures available at http://www.stsci.edu/~aconti/pixelz.html
The Astronomical Journal 07/2003; · 4.03 Impact Factor
