-
M. A. Lara-López,
A. M. Hopkins,
A. R. López-Sánchez,
S. Brough,
M. Colless J. Bland-Hawthorn,
S. Driver,
C. Foster,
J. Liske,
J. Loveday, A. S. G. Robotham,
R. G. Sharp,
O. Steele,
E. N. Taylor
[show abstract]
[hide abstract]
ABSTRACT: We study the interplay between gas phase metallicity (Z), specific star
formation rate (SSFR) and neutral hydrogen gas (HI) for galaxies of different
stellar masses. Our study uses spectroscopic data from GAMA and SDSS star
forming galaxies, as well as HI-detection from the ALFALFA and GASS public
catalogues. We present a model based on the Z-SSFR relation that shows that at
a given stellar mass, depending on the amount of gas, galaxies will follow
opposite behaviours. Low-mass galaxies with a large amount of gas will show
high SSFR and low metallicities, while low-mass galaxies with small amounts of
gas will show lower SSFR and high metallicities. In contrast, massive galaxies
with a large amount of gas will show moderate SSFR and high metallicities,
while massive galaxies with small amounts of gas will show low SSFR and low
metallicities. Using ALFALFA and GASS counterparts, we find that the amount of
gas is related to those drastic differences in Z and SSFR for galaxies of a
similar stellar mass.
04/2013;
-
M. W. Grootes,
R. J. Tuffs,
C. C. Popescu,
B. Pastrav,
E. Andrae,
M. Gunawardhana,
L. S. Kelvin,
J. Liske,
M. Seibert,
E. N. Taylor, [......],
S. Maddox,
B. F. Madore,
M. J. Michałowski,
P. Norberg,
H. R. Parkinson,
M. Prescott, A. S. G. Robotham,
D. J. B. Smith,
D. Thomas,
E. Valiante
[show abstract]
[hide abstract]
ABSTRACT: We report the discovery of a well-defined correlation between B-band face-on
central optical depth due to dust, \tau^f_B, and the stellar mass surface
density, \mu_{*}, of nearby (z < 0.13) spiral galaxies: log(\tau^f_B) =
1.12(+-0.11)log(\mu_{*}/M_sol kpc^2)-8.6(+-0.8). This relation was derived from
a sample of spiral galaxies taken from the Galaxy and Mass Assembly (GAMA)
survey and detected in the FIR/submm in the Herschel-ATLAS survey. Using a
quantitative analysis of the NUV attenuation-inclination relation for complete
samples of GAMA spirals categorized according to \mu_{*} we demonstrate that
this correlation can be used to statistically correct for dust attenuation
purely on the basis of optical photometry and S'ersic-profile morphological
fits. Considered together with previously established empirical relationships
between stellar mass, metallicity and gas mass, the near linearity and high
constant of proportionality of the \tau^f_B-\mu_{*} relation disfavors a
stellar origin for the bulk of refractory grains in spiral galaxies, instead
being consistent with the existence of a ubiquitous and very rapid mechanism
for the growth of dust in the ISM. We use the \tau^f_B-\mu_{*} relation in
conjunction with the radiation transfer model for spiral galaxies of Popescu &
Tuffs (2011) to derive intrinsic scaling relations between specific star
formation rate (sSFR), stellar mass, and \mu_{*}, in which the attenuation of
the UV light used to measure the SFR is corrected on an object-to-object basis.
A marked reduction in scatter in these relations is achieved which is
demonstrably due to correction of both the inclination-dependent and face-on
components of attenuation. Our results are consistent with a picture of spiral
galaxies in which most of the submm emission originates from grains residing in
translucent structures, exposed to UV in the diffuse interstellar radiation
field.
The Astrophysical Journal 03/2013; 766:59. · 6.02 Impact Factor
-
A. M. Hopkins,
S. P. Driver,
S. Brough,
M. S. Owers,
A. E. Bauer,
M. L. P. Gunawardhana,
M. E. Cluver,
M. Colless,
C. Foster,
M. A. Lara-Lopez, [......],
M. Seibert,
L. Staveley-Smith,
W. Sutherland,
E. Taylor,
L. Van Waerbeke,
J. A. Vazquez-Mata,
S. Warren,
D. B. Wijesinghe,
V. Wild,
S. Wilkins
[show abstract]
[hide abstract]
ABSTRACT: The Galaxy And Mass Assembly (GAMA) survey is a multiwavelength photometric
and spectroscopic survey, using the AAOmega spectrograph on the
Anglo-Australian Telescope to obtain spectra for up to ~300000 galaxies over
280 square degrees, to a limiting magnitude of r_pet < 19.8 mag. The target
galaxies are distributed over 0<z<0.5 with a median redshift of z~0.2, although
the redshift distribution includes a small number of systems, primarily
quasars, at higher redshifts, up to and beyond z=1. The redshift accuracy
ranges from sigma_v~50km/s to sigma_v~100km/s depending on the signal-to-noise
of the spectrum. Here we describe the GAMA spectroscopic reduction and analysis
pipeline. We present the steps involved in taking the raw two-dimensional
spectroscopic images through to flux-calibrated one-dimensional spectra. The
resulting GAMA spectra cover an observed wavelength range of 3750<lambda<8850 A
at a resolution of R~1300. The final flux calibration is typically accurate to
10-20%, although the reliability is worse at the extreme wavelength ends, and
poorer in the blue than the red. We present details of the measurement of
emission and absorption features in the GAMA spectra. These measurements are
characterised through a variety of quality control analyses detailing the
robustness and reliability of the measurements. We illustrate the quality of
the measurements with a brief exploration of elementary emission line
properties of the galaxies in the GAMA sample. We demonstrate the luminosity
dependence of the Balmer decrement, consistent with previously published
results, and explore further how Balmer decrement varies with galaxy mass and
redshift. We also investigate the mass and redshift dependencies of the
[NII]/Halpha vs [OIII]/Hbeta spectral diagnostic diagram, commonly used to
discriminate between star forming and nuclear activity in galaxies.
01/2013;
-
A. S. G. Robotham,
J. Liske,
S. P. Driver,
A. E. Sansom,
I. K. Baldry,
A. E. Bauer,
J. Bland-Hawthorn,
S. Brough,
M. J. I. Brown,
M. Colless, [......],
M. J. Drinkwater,
M. W. Grootes,
A. M. Hopkins,
L. S. Kelvin,
P. Norberg,
J. Loveday,
S. Phillipps,
R. Sharp,
E. N. Taylor,
R. J. Tuffs
[show abstract]
[hide abstract]
ABSTRACT: In this work we investigate in detail the effects local environment (groups
and pairs) has on galaxies with stellar mass similar to the Milky-Way (L*
galaxies). A volume limited sample of 6,150 galaxies is classified to determine
emission features, morphological type and presence of a disk. This sample
allows for characteristics of galaxies to be isolated (e.g. stellar mass and
group halo mass), and their codependencies determined.
We observe that galaxy-galaxy interactions play the most important role in
shaping the evolution within a group halo, the main role of halo mass is in
gathering the galaxies together to encourage such interactions. Dominant pair
galaxies find their overall star formation enhanced when the pair's mass ratio
is close to 1, otherwise we observe the same galaxies as we would in an
unpaired system. The minor galaxy in a pair is greatly affected by its
companion galaxy, and whilst the star forming fraction is always suppressed
relative to equivalent stellar mass unpaired galaxies, it becomes lower still
when the mass ratio of a pair system increases.
We find that, in general, the close galaxy-galaxy interaction rate drops as a
function of halo mass for a given amount of stellar mass. We find evidence of a
local peak of interactions for Milky-Way stellar mass galaxies in Milky-Way
halo mass groups. Low mass halos, and in particular Local Group mass halos, are
an important environment for understanding the typical evolutionary path of a
unit of stellar mass.
We find compelling evidence for galaxy conformity in both groups and pairs,
where morphological type conformity is dominant in groups, and emission class
conformity is dominant in pairs. This suggests that group scale conformity is
the result of many galaxy encounters over an extended period of time, whilst
pair conformity is a fairly instantaneous response to a transitory interaction.
01/2013;
-
S ~P Driver, A ~S ~G Robotham,
L Kelvin,
M Alpaslan,
I ~K Baldry,
S ~P Bamford,
S Brough,
M Brown,
A ~M Hopkins,
J Liske, [......],
M Prescott,
M Seibert,
R ~G Sharp,
W ~J Sutherland,
E ~N Taylor,
D Thomas,
R ~J Tuffs,
E Kampen,
D Wijesinghe,
S Wilkins
mnras. 12/2012; 427:3244-3264.
-
M. J. Hardcastle,
J. H. Y. Ching,
J. S. Virdee,
M. J. Jarvis,
S. M. Croom,
E. M. Sadler,
T. Mauch,
D. J. B. Smith,
J. A. Stevens,
M. Baes, [......],
S. Eales,
R. Hopwood,
J. Liske,
S. Maddox,
M. J. Michalowski,
E. E. Rigby, A. S. G. Robotham,
O. Steele,
D. Thomas,
E. Valiante
[show abstract]
[hide abstract]
ABSTRACT: We have constructed a sample of radio-loud objects with optical spectroscopy
from the Galaxy and Mass Assembly (GAMA) project over the Herschel-ATLAS Phase
1 fields. Classifying the radio sources in terms of their optical spectra, we
find that strong-emission-line sources (`high-excitation radio galaxies') have,
on average, a factor ~4 higher 250-micron Herschel luminosity than weak-line
(`low-excitation') radio galaxies and are also more luminous than
magnitude-matched radio-quiet galaxies at the same redshift. Using all five
H-ATLAS bands, we show that this difference in luminosity between the
emission-line classes arises mostly from a difference in the average dust
temperature; strong-emission-line sources tend to have comparable dust masses
to, but higher dust temperatures than, radio galaxies with weak emission lines.
We interpret this as showing that radio galaxies with strong nuclear emission
lines are much more likely to be associated with star formation in their host
galaxy, although there is certainly not a one-to-one relationship between star
formation and strong-line AGN activity. The strong-line sources are estimated
to have star-formation rates at least a factor 3-4 higher than those in the
weak-line objects. Our conclusion is consistent with earlier work, generally
carried out using much smaller samples, and reinforces the general picture of
high-excitation radio galaxies as being located in lower-mass, less evolved
host galaxies than their low-excitation counterparts.
11/2012;
-
S. P. Driver, A. S. G. Robotham,
L. Kelvin,
M. Alpaslan,
I. K. Baldry,
S. P. Bamford,
S. Brough,
M. Brown,
A. M. Hopkins,
J. Liske, [......],
M. Prescott,
M. Seibert,
R. G. Sharp,
W. J. Sutherland,
E. N. Taylor,
D. Thomas,
R. J. Tuffs,
E. van Kampen,
D. Wijesinghe,
S. Wilkins
[show abstract]
[hide abstract]
ABSTRACT: We use the GAMA I dataset combined with GALEX, SDSS and UKIDSS imaging to
construct the low-redshift (z<0.1) galaxy luminosity functions in FUV, NUV,
ugriz, and YJHK bands from within a single well constrained volume of 3.4 x
10^5 (Mpc/h)^{3}. The derived luminosity distributions are normalised to the
SDSS DR7 main survey to reduce the estimated cosmic variance to the 5 per cent
level. The data are used to construct the cosmic spectral energy distribution
(CSED) from 0.1 to 2.1 \mum free from any wavelength dependent cosmic variance
for both the elliptical and non-elliptical populations. The two populations
exhibit dramatically different CSEDs as expected for a predominantly old and
young population respectively. Using the Driver et al. (2008) prescription for
the azimuthally averaged photon escape fraction, the non-ellipticals are
corrected for the impact of dust attenuation and the combined CSED constructed.
The final results show that the Universe is currently generating (1.8 +/- 0.3)
x 10^{35} h W Mpc^{-3} of which (1.2 +/- 0.1) x 10^{35} h W Mpc^{-3} is
directly released into the inter-galactic medium and (0.6 +/- 0.1) x 10^{35} h
W Mpc^{-3} is reprocessed and reradiated by dust in the far-IR. Using the GAMA
data and our dust model we predict the mid and far-IR emission which agrees
remarkably well with available data. We therefore provide a robust description
of the pre- and post dust attenuated energy output of the nearby Universe from
0.1micron to 0.6mm. The largest uncertainty in this measurement lies in the mid
and far-IR bands stemming from the dust attenuation correction and its
currently poorly constrained dependence on environment, stellar mass, and
morphology.
09/2012;
-
A ~S ~G Robotham,
I ~K Baldry,
J Bland-Hawthorn,
S ~P Driver,
J Loveday,
P Norberg,
A ~E Bauer,
K Bekki,
S Brough,
M Brown,
A Graham,
A ~M Hopkins,
S Phillipps,
C Power,
A Sansom,
L Staveley-Smith
[show abstract]
[hide abstract]
ABSTRACT: Analysing all Galaxy and Mass Assembly (GAMA) galaxies within a factor two
(+/- 0.3 dex) of the stellar mass of the Milky Way (MW), there is a 11.9%
chance that one of these galaxies will have a close companion (within a
projected separation of 70 kpc and radial separation of 400 km/s) that is at
least as massive as the Large Magellanic Cloud (LMC). Two close companions at
least as massive as the Small Magellanic Cloud (SMC) are rare at the 3.4%
level. Two full analogues to the MW- LMC-SMC system were found in GAMA (all
galaxies late-type and star forming), suggesting such a combination of close
together, late-type, star-forming galaxies is rare: only 0.4% of MW mass
galaxies (in the range where we could observe both the LMC and SMC) have such a
system. In summary, the MW-LMC-SMC system is a 2.7? event (when recast into
Gaussian statistics).
Using cross-correlation comparisons we find that there is a preference for
SMC- LMC binary pair analogues to be located within 2 Mpc of a range of
different lumi- nosity groups. There is a particular preference is for such
binaries to be located near LG luminosity systems. When these groups are
subdivided into small magnitude gap and large magnitude gap subsets, the
binaries prefer to be spatially associated with the small magnitude gap
systems. These systems will be dynamically less evolved, but still offer the
same amount of gravitational dark matter. This suggests that binaries such as
the SMC-LMC might be transient systems, usually destroyed during vigorous
merger events. Details of a particularly striking analogue to the MW-SMC-LMC
and M31 complex are included.
mnras. 08/2012; 424:1448-1453.
-
L. Christodoulou,
C. Eminian,
J. Loveday,
P. Norberg,
I. K. Baldry,
P. D. Hurley,
S. P. Driver,
S. P. Bamford,
A. M. Hopkins,
J. Liske, [......],
C. C. Popescu,
M. Prescott, A. S. G. Robotham,
R. G. Sharp,
W. J. Sutherland,
E. N. Taylor,
D. Thomas,
R. J. Tuffs,
E. van Kampen,
D. Wijesinghe
[show abstract]
[hide abstract]
ABSTRACT: We measure the two-point angular correlation function of a sample of
4,289,223 galaxies with r < 19.4 mag from the Sloan Digital Sky Survey as a
function of photometric redshift, absolute magnitude and colour down to M_r -
5log h = -14 mag. Photometric redshifts are estimated from ugriz model
magnitudes and two Petrosian radii using the artificial neural network package
ANNz, taking advantage of the Galaxy and Mass Assembly (GAMA) spectroscopic
sample as our training set. The photometric redshifts are then used to
determine absolute magnitudes and colours. For all our samples, we estimate the
underlying redshift and absolute magnitude distributions using Monte-Carlo
resampling. These redshift distributions are used in Limber's equation to
obtain spatial correlation function parameters from power law fits to the
angular correlation function. We confirm an increase in clustering strength for
sub-L* red galaxies compared with ~L* red galaxies at small scales in all
redshift bins, whereas for the blue population the correlation length is almost
independent of luminosity for ~L* galaxies and fainter. A linear relation
between relative bias and log luminosity is found to hold down to luminosities
L~0.03L*. We find that the redshift dependence of the bias of the L* population
can be described by the passive evolution model of Tegmark & Peebles (1998). A
visual inspection of a random sample of our r < 19.4 sample of SDSS galaxies
reveals that about 10 per cent are spurious, with a higher contamination rate
towards very faint absolute magnitudes due to over-deblended nearby galaxies.
We correct for this contamination in our clustering analysis.
06/2012;
-
D. B. Wijesinghe,
A. M. Hopkins,
S. Brough,
E. N. Taylor,
P. Norberg,
A. Bauer,
M. J. I. Brown,
E. Cameron,
C. J. Conselice,
S. Croom, [......],
C. C. Popescu,
M. Prescott,
R. Sharp,
I. Baldry,
E. M. Sadler,
J. Liske, A. S. G. Robotham,
S. Bamford,
J. Bland-Hawthorn,
M. Gunawardhana
[show abstract]
[hide abstract]
ABSTRACT: We present a detailed investigation into the effects of galaxy environment on
their star formation rates (SFR) using galaxies observed in the Galaxy and Mass
Assembly Survey (GAMA). We use three independent volume-limited samples of
galaxies within z < 0.2 and Mr < -17.8. We investigate the known SFR-density
relationship and explore in detail the dependence of SFR on stellar mass and
density. We show that the SFR-density trend is only visible when we include the
passive galaxy population along with the star-forming population. This
SFR-density relation is absent when we consider only the star-forming
population of galaxies, consistent with previous work. While there is a strong
dependence of the EWH?a on density we find, as in previous studies, that these
trends are largely due to the passive galaxy population and this relationship
is absent when considering a "star-forming" sample of galaxies. We find that
stellar mass has the strongest influence on SFR and EWH?a with the environment
having no significant effect on the star-formation properties of the star
forming population. We also show that the SFR-density relationship is absent
for both early and late-type star-forming galaxies. We conclude that the
stellar mass has the largest impact on the current SFR of a galaxy, and any
environmental effect is not detectable. The observation that the trends with
density are due to the changing morphology fraction with density implies that
the timescales must be very short for any quenching of the SFR in infalling
galaxies. Alternatively galaxies may in fact undergo predominantly in-situ
evolution where the infall and quenching of galaxies from the field into dense
environments is not the dominant evolutionary mode.
05/2012;
-
N. Bourne,
S. J. Maddox,
L. Dunne,
R. Auld,
M. Baes,
I. K. Baldry,
D. G. Bonfield,
A. Cooray,
S. M. Croom,
A. Dariush, [......],
R. Hopwood,
R. J. Ivison,
D. H. Jones,
L. S. Kelvin,
J. Liske,
J. Loveday,
P. Norberg, A. S. G. Robotham,
G. Rodighiero,
P. Temi
[show abstract]
[hide abstract]
ABSTRACT: We use the Herschel-ATLAS survey to conduct the first large-scale statistical
study of the submm properties of optically selected galaxies. Using ~80,000
r-band selected galaxies from 126 deg^2 of the GAMA survey, we stack into submm
imaging at 250, 350 and 500{\mu}m to gain unprecedented statistics on the dust
emission from galaxies at z < 0.35. We find that low redshift galaxies account
for 5% of the cosmic 250{\mu}m background (4% at 350{\mu}m; 3% at 500{\mu}m),
of which approximately 60% comes from 'blue' and 20% from 'red' galaxies
(rest-frame g - r). We compare the dust properties of different galaxy
populations by dividing the sample into bins of optical luminosity, stellar
mass, colour and redshift. In blue galaxies we find that dust temperature and
luminosity correlate strongly with stellar mass at a fixed redshift, but red
galaxies do not follow these correlations and overall have lower luminosities
and temperatures. We make reasonable assumptions to account for the
contaminating flux from lensing by red sequence galaxies and conclude that
galaxies with different optical colours have fundamentally different dust
emission properties. Results indicate that while blue galaxies are more
luminous than red galaxies due to higher temperatures, the dust masses of the
two samples are relatively similar. Dust mass is shown to correlate with
stellar mass, although the dust/stellar mass ratio is much higher for low
stellar mass galaxies, consistent with the lowest mass galaxies having the
highest specific star formation rates. We stack the 250{\mu}m/NUV luminosity
ratio, finding results consistent with greater obscuration of star formation at
lower stellar mass and higher redshift. Submm luminosities and dust masses of
all galaxies are shown to evolve strongly with redshift, indicating a fall in
the amount of obscured star formation in ordinary galaxies over the last four
billion years.
01/2012;
-
J Loveday,
P Norberg,
I K Baldry,
S P Driver,
A M Hopkins,
J A Peacock,
S P Bamford,
J Liske,
J Bland-Hawthorn,
S Brough, [......],
C C Popescu,
M Prescott, A S G Robotham,
R G Sharp,
W J Sutherland,
E N Taylor,
D Thomas,
R J Tuffs,
E Van Kampen,
D Wijesinghe
[show abstract]
[hide abstract]
ABSTRACT: Galaxy and Mass Assembly (GAMA) is a project to study galaxy formation and evolution, combining imaging data from ultraviolet to radio with spectroscopic data from the AAOmega spectrograph on the Anglo-Australian Telescope. Using data from phase 1 of GAMA, taken over three observing seasons, and correcting for various minor sources of incompleteness, we calculate galaxy luminosity functions (LFs) and their evolution in the ugriz passbands. At low redshift, z < 0.1, we find that blue galaxies, defined according to a magnitude-dependent but non-evolving colour cut, are reasonably well fitted over a range of more than ten magnitudes by simple Schechter functions in all bands. Red galaxies, and the combined blue-plus-red sample, require double power-law Schechter functions to fit a dip in their LF faintwards of the characteristic magnitude M * before a steepening faint end. This upturn is at least partly due to dust-reddened disc galaxies. We measure evolution of the galaxy LF over the redshift range 0.002 < z < 0.5 both by using a parametric fit and by measuring binned LFs in redshift slices. The characteristic lumi-nosity L * is found to increase with redshift in all bands, with red galaxies showing stronger luminosity evolution than blue galaxies. The comoving number density of blue galaxies in-creases with redshift, while that of red galaxies decreases, consistent with prevailing move- 2 J. Loveday et al. ment from blue cloud to red sequence. As well as being more numerous at higher redshift, blue galaxies also dominate the overall luminosity density beyond redshifts z 0.2. At lower redshifts, the luminosity density is dominated by red galaxies in the riz bands, by blue galax-ies in u and g.
Mon. Not. R. Astron. Soc. 12/2011; 000:0-0.
-
I. K. Baldry,
S. P. Driver,
J. Loveday,
E. N. Taylor,
L. S. Kelvin,
J. Liske,
P. Norberg, A. S. G. Robotham,
S. Brough,
A. M. Hopkins, [......],
J. A. Peacock,
J. Bland-Hawthorn,
C. J. Conselice,
S. M. Croom,
D. H. Jones,
H. R. Parkinson,
C. C. Popescu,
M. Prescott,
R. G. Sharp,
R. J. Tuffs
[show abstract]
[hide abstract]
ABSTRACT: We determine the low-redshift field galaxy stellar mass function (GSMF) using
an area of 143 deg^2 from the first three years of the Galaxy And Mass Assembly
(GAMA) survey. The magnitude limits of this redshift survey are r < 19.4 mag
over two thirds and 19.8 mag over one third of the area. The GSMF is determined
from a sample of 5210 galaxies using a density-corrected maximum volume method.
This efficiently overcomes the issue of fluctuations in the number density
versus redshift. With H_0 = 70, the GSMF is well described between 10^8 and
10^11.5 Msun using a double Schechter function with mass^* = 10^10.66 Msun,
phi_1^* = 3.96 x 10^-3 Mpc^-3, alpha_1 = -0.35, phi_2^* = 0.79 x 10^-3 Mpc^-3
and alpha_2 = -1.47. This result is more robust to uncertainties in the
flow-model corrected redshifts than from the shallower Sloan Digital Sky Survey
main sample (r < 17.8 mag). The upturn in the GSMF is also seen directly in the
i-band and K-band galaxy luminosity functions. Accurately measuring the GSMF
below 10^8 Msun is possible within the GAMA survey volume but as expected
requires deeper imaging data to address the contribution from low
surface-brightness galaxies.
Mon.Not.Roy.Astron.Soc. 11/2011; 421.
-
Matthew Prescott,
I. K. Baldry,
P. A. James,
S. P. Bamford,
J. Bland-Hawthorn,
S. Brough,
M. J. I. Brown,
E. Cameron,
C. J. Conselice,
S. M. Croom, [......],
S. Phillipps,
K. A. Pimbblet,
C. C. Popescu, A. S. G. Robotham,
R. G. Sharp,
W. J. Sutherland,
E. N. Taylor,
R. J. Tuffs,
E. van Kampen,
D. Wijesinghe
[show abstract]
[hide abstract]
ABSTRACT: We investigate the properties of satellite galaxies that surround isolated
hosts within the redshift range 0.01 < z < 0.15, using data taken as part of
the Galaxy And Mass Assembly survey. Making use of isolation and satellite
criteria that take into account stellar mass estimates, we find 3514 isolated
galaxies of which 1426 host a total of 2998 satellites. Separating the red and
blue populations of satellites and hosts, using colour-mass diagrams, we
investigate the radial distribution of satellite galaxies and determine how the
red fraction of satellites varies as a function of satellite mass, host mass
and the projected distance from their host. Comparing the red fraction of
satellites to a control sample of small neighbours at greater projected radii,
we show that the increase in red fraction is primarily a function of host mass.
The satellite red fraction is about 0.2 higher than the control sample for
hosts with 11.0 < log M_* < 11.5, while the red fractions show no difference
for hosts with 10.0 < log M_* < 10.5. For the satellites of more massive hosts
the red fraction also increases as a function of decreasing projected distance.
Our results suggest that the likely main mechanism for the quenching of star
formation in satellites hosted by isolated galaxies is strangulation.
07/2011;
-
A. Dariush,
L. Cortese,
S. Eales,
E. Pascale,
M. W. L. Smith,
L. Dunne,
S. Dye,
D Scott,
R. Auld,
M. Baes, [......],
C. C. Popescu, A. S. G. Robotham,
G. Rodighiero,
M. Prescott,
E. Rigby,
M. Seibert,
D. J. B. Smith,
P. Temi,
R. J. Tuffs,
P. van der Werf
[show abstract]
[hide abstract]
ABSTRACT: We investigate the ultraviolet and optical properties and environment of low
redshift galaxies detected in the Herschel Astrophysical Terahertz Large Area
Survey (H-ATLAS) science demonstration data. We use the Sloan Digital Sky
Survey seventh release and the Galaxy And Mass Assembly database to select
galaxies with r_Petro < 19.0 mag in the redshift range 0.02 < z < 0.2 and look
for their submillimeter counterparts in H-ATLAS. Our results show that at low
redshift, H-ATLAS detects mainly blue/star-forming galaxies with a minor
contribution from red systems which are highly obscured by dust. In addition we
find that the colour of a galaxy rather than the local density of its
environment determines whether it is detectable by H-ATLAS. The average dust
temperature of galaxies that are simultaneously detected by both PACS and SPIRE
is 25K \pm 4K, independent of environment. This analysis provides a glimpse of
the potential of the H-ATLAS data to investigate the submillimeter properties
of galaxies in the local universe.
06/2011;
-
A. S. G. Robotham,
P. Norberg,
S. P. Driver,
I. K. Baldry,
S. P. Bamford,
A. M. Hopkins,
J. Liske,
J. Loveday,
A. Merson,
J. A. Peacock, [......],
S. Phillipps,
C. C. Popescu,
M. Prescott,
R. G. Sharp,
W. J. Sutherland,
E. N. Taylor,
D Thomas,
R. J. Tuffs,
E. van Kampen,
D. Wijesinghe
[show abstract]
[hide abstract]
ABSTRACT: Using the complete GAMA-I survey covering ~142 sq. deg. to r=19.4, of which
~47 sq. deg. is to r=19.8, we create the GAMA-I galaxy group catalogue (G3Cv1),
generated using a friends-of-friends (FoF) based grouping algorithm. Our
algorithm has been tested extensively on one family of mock GAMA lightcones,
constructed from Lambda-CDM N-body simulations populated with semi-analytic
galaxies. Recovered group properties are robust to the effects of interlopers
and are median unbiased in the most important respects. G3Cv1 contains 14,388
galaxy groups (with multiplicity >= 2$), including 44,186 galaxies out of a
possible 110,192 galaxies, implying ~40% of all galaxies are assigned to a
group. The similarities of the mock group catalogues and G3Cv1 are multiple:
global characteristics are in general well recovered. However, we do find a
noticeable deficit in the number of high multiplicity groups in GAMA compared
to the mocks. Additionally, despite exceptionally good local spatial
completeness, G3Cv1 contains significantly fewer compact groups with 5 or more
members, this effect becoming most evident for high multiplicity systems. These
two differences are most likely due to limitations in the physics included of
the current GAMA lightcone mock. Further studies using a variety of galaxy
formation models are required to confirm their exact origin.
06/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: We calculate the local ultraviolet (UV) flux density in the Galaxy Evolution Explorer (GALEX) Medium Imaging Survey (MIS) far-UV (FUV) and near-UV (NUV) bands using redshifts provided by Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7). Luminosity functions are calculated for the overlapping MIS and SDSS sample, allowing flux densities to be measured and the local star formation rate (SFR) to be calculated using volumes much larger than previous FUV-based estimates. We calculate flux densities for a dust-corrected low-redshift (0.013 ≤ z ≤ 0.1) sample of fν–FUV= 22.24 ± 3.13 × 1025 h erg s−1 Hz−1 Mpc−3, fν–NUV= 38.54 ± 5.30 × 1025 h erg s−1 Hz−1 Mpc−3. The SFR density found is 0.0312 ± 0.0045 h M⊙ yr−1 Mpc−3. This is larger than published rates recently found using the UV implied SFR, though the major discrepancy is the correction made for dust attenuation and once this is dealt with consistently the results agree well. These values are also consistent with recent Hα derived SFRs. Once cosmic variance is taken into account most of the recent SFRs at low redshift (z ≤ 0.3) found in the literature can be brought into agreement, however, the lowest redshift values (z ≤ 0.045) do appear to be significantly lower.
Monthly Notices of the Royal Astronomical Society 05/2011; 413(4):2570 - 2582. · 4.90 Impact Factor
-
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
-
S. Brough,
A. M. Hopkins,
R. G. Sharp,
M. Gunawardhana,
D. Wijesinghe, A. S. G. Robotham,
S. P. Driver,
I. K. Baldry,
S. P. Bamford,
J. Liske, [......],
R. C. Nichol,
H. R. Parkinson,
K. Pimbblet,
C. C. Popescu,
M. Prescott,
W. J. Sutherland,
E. Taylor,
D Thomas,
R. J. Tuffs,
E. van Kampen
[show abstract]
[hide abstract]
ABSTRACT: We present an analysis of the properties of the lowest Halpha-luminosity galaxies (L_Halpha<4x10^32 W; SFR<0.02 Msun/yr) in the Galaxy And Mass Assembly (GAMA) survey. These galaxies make up the the rise above a Schechter function in the number density of systems seen at the faint end of the Halpha luminosity function. Above our flux limit we find that these galaxies are principally composed of intrinsically low stellar mass systems (median stellar mass =2.5x10^8 Msun) with only 5/90 having stellar masses M>10^10 Msun. The low SFR systems are found to exist predominantly in the lowest density environments (median density ~0.02 galaxy Mpc^-2 with none in environments more dense than ~1.5 galaxy Mpc^-2). Their current specific star formation rates (SSFR; -8.5 < log(SSFR[yr^-1])<-12.) are consistent with their having had a variety of star formation histories. The low density environments of these galaxies demonstrates that such low-mass, star-forming systems can only remain as low-mass and forming stars if they reside sufficiently far from other galaxies to avoid being accreted, dispersed through tidal effects or having their gas reservoirs rendered ineffective through external processes. Comment: 10 pages, accepted for publication in MNRAS
12/2010;
-
M. J. Hardcastle,
J. S. Virdee,
M. J. Jarvis,
D. G. Bonfield,
L. Dunne,
S. Rawlings,
J. A. Stevens,
N. M. Christopher,
I. Heywood,
T. Mauch, [......],
M. Pohlen,
M. Prescott,
E. E. Rigby, A. S. G. Robotham,
G. Rodighiero,
D. Scott,
R. Sharp,
D. J. B. Smith,
P. Temi,
E. van Kampen
[show abstract]
[hide abstract]
ABSTRACT: We use the Herschel-Astrophysical Terahertz Large Area Survey (ATLAS) science demonstration data to investigate the star formation properties of radio-selected galaxies in the GAMA-9h field as a function of radio luminosity and redshift. Radio selection at the lowest radio luminosities, as expected, selects mostly starburst galaxies. At higher radio luminosities, where the population is dominated by active galactic nuclei (AGN), we find that some individual objects are associated with high far-infrared luminosities. However, the far-infrared properties of the radio-loud population are statistically indistinguishable from those of a comparison population of radio-quiet galaxies matched in redshift and K-band absolute magnitude. There is thus no evidence that the host galaxies of these largely low-luminosity (Fanaroff–Riley class I), and presumably low-excitation, AGN, as a population, have particularly unusual star formation histories. Models in which the AGN activity in higher luminosity, high-excitation radio galaxies is triggered by major mergers would predict a luminosity-dependent effect that is not seen in our data (which only span a limited range in radio luminosity) but which may well be detectable with the full Herschel-ATLAS data set.
Monthly Notices of the Royal Astronomical Society 11/2010; 409(1):122 - 131. · 4.90 Impact Factor
