1,140 research outputs found
Reflections of Cluster Assembly in the Stellar Populations and Dynamics of Member Galaxies
We combine optical (HST) and UV (GALEX) imaging of two intermediate redshift galaxy clusters with spectroscopy of member galaxies, to study the relation between the formation history of cluster galaxies and the assembly history of the cluster structure itself. We identify key differences in the large-scale structure and intracluster medium properties of each cluster. In order to assess the importance of cluster substructure and the ICM in the evolution of cluster galaxies, we examine several key indicators of the recent star-formation and assembly history of cluster galaxies. We find that galaxies in cluster MS 0451 (z = 0.54) exhibit a markedly lower incidence of recent star formation activity than galaxies in cluster Cl 0024 (z = 0.39), likely the result of starvation by the ICM. In addition, Cl 0024 members show evidence for kinematic disturbances that can be linked to the assembly of substructure
The GALEX Arecibo SDSS Survey. VIII. Final Data Release -- The Effect of Group Environment on the Gas Content of Massive Galaxies
We present the final data release from the GALEX Arecibo SDSS Survey (GASS),
a large Arecibo program that measured the HI properties for an unbiased sample
of ~800 galaxies with stellar masses greater than 10^10 Msun and redshifts
0.025<z<0.05. This release includes new Arecibo observations for 250 galaxies.
We use the full GASS sample to investigate environmental effects on the cold
gas content of massive galaxies at fixed stellar mass. The environment is
characterized in terms of dark matter halo mass, obtained by cross-matching our
sample with the SDSS group catalog of Yang et al. Our analysis provides, for
the first time, clear statistical evidence that massive galaxies located in
halos with masses of 10^13-10^14 Msun have at least 0.4 dex less HI than
objects in lower density environments. The process responsible for the
suppression of gas in group galaxies most likely drives the observed quenching
of the star formation in these systems. Our findings strongly support the
importance of the group environment for galaxy evolution, and have profound
implications for semi-analytic models of galaxy formation, which currently do
not allow for stripping of the cold interstellar medium in galaxy groups.Comment: 36 pages, 16 figures. Accepted for publication in MNRAS. Version with
supplementary material available at
http://www.mpa-garching.mpg.de/GASS/pubs.php . GASS released data can be
found at http://www.mpa-garching.mpg.de/GASS/data.ph
GALEX Observations of "Passive Spirals" in the Cluster Cl 0024+17: Clues to the Formation of S0 Galaxies
We present new results from deep GALEX UV imaging of the cluster Cl 0024+17
at z~0.4. Rest-frame far UV emission is detected from a large fraction of
so-called ``passive spiral galaxies'' -a significant population which exhibits
spiral morphology with little or no spectroscopic evidence for ongoing star
formation. This population is thought to represent infalling galaxies whose
star formation has been somehow truncated by environmental processes, possibly
in morphological transition to S0 galaxies. Compared to normal cluster spirals,
we find that passive spirals are redder in FUV-optical color, while exhibiting
much stronger UV emission than cluster E/S0s - as expected for
recently-truncated star formation. By modeling the different temporal
sensitivities of UV and spectroscopic data to recent activity, we show that
star formation in passive spirals decayed on timescales of less than 1 Gyr,
consistent with `gas starvation' - a process where the cluster environment
prevents cold gas from accreting onto the spiral disk. Intriguingly, the
fraction of spirals currently observed in the passive phase is consistent with
the longer period expected for the morphological transformation and the
subsequent build-up of cluster S0s observed since z=0.4.Comment: 5 pages, 3 figures, ApJL accepte
The GALEX Arecibo SDSS survey: III. Evidence for the Inside-Out Formation of Galactic Disks
We analyze a sample of galaxies with stellar masses greater than and with redshifts in the range for which HI mass
measurements are available from the GALEX Arecibo SDSS Survey (GASS) or from
the Arecibo Legacy Fast ALFA survey (ALFALFA). At a given value of , our
sample consists primarily of galaxies that are more HI-rich than average. We
constructed a series of three control samples for comparison with these HI-rich
galaxies. As expected, HI-rich galaxies differ strongly from galaxies of same
stellar mass that are selected without regard to HI content. The majority of
these differences are attributable to the fact that galaxies with more gas are
bluer and more actively star-forming. In order to identify those galaxy
properties that are causally connected with HI content, we compare results
derived for the HI sample with those derived for galaxies matched in stellar
mass, size and NUV- colour. The only photometric property that is clearly
attributable to increasing HI content, is the colour gradient of the galaxy.
Galaxies with larger HI fractions have bluer, more actively star-forming outer
disks compared to the inner part of the galaxy. HI-rich galaxies also have
larger -band radii compared to -band radii. Our results are consistent
with the "inside-out" picture of disk galaxy formation, which has commonly
served as a basis for semi-analytic models of the formation of disks in the
context of Cold Dark Matter cosmologies. The lack of any intrinsic connection
between HI fraction and galaxy asymmetry suggests that gas is accreted smoothly
onto the outer disk.Comment: 18 pages, 20 figures. Accepted for publication in MNRAS. GASS
publications and released data can be found at
http://www.mpa-garching.mpg.de/GASS/index.ph
The GALEX Arecibo SDSS Survey. IV. Baryonic Mass-Velocity-Size Relations of Massive Galaxies
We present dynamical scaling relations for a homogeneous and representative
sample of ~500 massive galaxies, selected only by stellar mass (>10^10 Msun)
and redshift (0.025<z<0.05) as part of the ongoing GALEX Arecibo SDSS Survey.
We compare baryonic Tully-Fisher (BTF) and Faber-Jackson (BFJ) relations for
this sample, and investigate how galaxies scatter around the best fits obtained
for pruned subsets of disk-dominated and bulge-dominated systems. The BFJ
relation is significantly less scattered than the BTF when the relations are
applied to their maximum samples, and is not affected by the inclination
problems that plague the BTF. Disk-dominated, gas-rich galaxies systematically
deviate from the BFJ relation defined by the spheroids. We demonstrate that by
applying a simple correction to the stellar velocity dispersions that depends
only on the concentration index of the galaxy, we are able to bring disks and
spheroids onto the same dynamical relation -- in other words, we obtain a
generalized BFJ relation that holds for all the galaxies in our sample,
regardless of morphology, inclination or gas content, and has a scatter smaller
than 0.1 dex. We find that disks and spheroids are offset in the stellar
dispersion-size relation, and that the offset is removed when corrected
dispersions are used instead. The generalized BFJ relation represents a
fundamental correlation between the global dark matter and baryonic content of
galaxies, which is obeyed by all (massive) systems regardless of morphology.
[abridged]Comment: 20 pages, 15 figures. Accepted for publication in MNRAS. GASS
publications and released data can be found at
http://www.mpa-garching.mpg.de/GASS/index.ph
The Evolutionary History of Galactic Bulges: Photometric and Spectroscopic Studies of Distant Spheroids in the GOODS Fields
We report on the first results of a new study aimed at understanding the
diversity and evolutionary history of distant galactic bulges in the context of
now well-established trends for pure spheroidal galaxies. To this end, bulges
have been isolated for a sample of 137 spiral galaxies within the redshift
range 0.1<z<1.2 in the GOODS fields. Using proven photometric techniques we
determine the characteristic parameters (size, surface brightness, profile
shape) of both the disk and bulge components in our sample. In agreement with
earlier work which utilized aperture colors, distant bulges show a broader
range of optical colors than would be the case for passively-evolving
populations. To quantify the amount of recent star formation necessary to
explain this result, we used the DEIMOS spectrograph to secure stellar velocity
dispersions for a sizeable fraction of our sample. This has enabled us to
compare the Fundamental Plane of our distant bulges with that for spheroidal
galaxies in a similar redshift range. Bulges of spiral galaxies with a
bulge-to-total luminosity ratio (B/T)>0.2 show very similar patterns of
evolution to those seen for pure spheroidals such that the stellar populations
of all spheroids with M>10^{11}Msun are homogeneously old, consistent with a
single major burst of star formation at high redshift (z_f<~2), while bulges
with M<10^{11}Msun must have had more recent stellar mass growth (~10% in mass
since z~1). Although further data spanning a wider range of redshift and mass
is desirable, the striking similarity between the assembly histories of bulges
and low mass spheroidals is difficult to reconcile with the picture whereby the
majority of large bulges form primarily via secular processes within spiral
galaxies.Comment: 32 pages, 13 embedded color figures, uses emulateapj.cls. Submitted
to ApJ. High-resolution version available at
http://www.astro.caltech.edu/~lam/MacArthur_bulges.pdf (strongly recommended
COLD GASS, an IRAM legacy survey of molecular gas in massive galaxies: I. Relations between H2, HI, stellar content and structural properties
We are conducting COLD GASS, a legacy survey for molecular gas in nearby
galaxies. Using the IRAM 30m telescope, we measure the CO(1-0) line in a sample
of ~350 nearby (D=100-200 Mpc), massive galaxies (log(M*/Msun)>10.0). The
sample is selected purely according to stellar mass, and therefore provides an
unbiased view of molecular gas in these systems. By combining the IRAM data
with SDSS photometry and spectroscopy, GALEX imaging and high-quality Arecibo
HI data, we investigate the partition of condensed baryons between stars,
atomic gas and molecular gas in 0.1-10L* galaxies. In this paper, we present CO
luminosities and molecular hydrogen masses for the first 222 galaxies. The
overall CO detection rate is 54%, but our survey also uncovers the existence of
sharp thresholds in galaxy structural parameters such as stellar mass surface
density and concentration index, below which all galaxies have a measurable
cold gas component but above which the detection rate of the CO line drops
suddenly. The mean molecular gas fraction MH2/M* of the CO detections is
0.066+/-0.039, and this fraction does not depend on stellar mass, but is a
strong function of NUV-r colour. Through stacking, we set a firm upper limit of
MH2/M*=0.0016+/-0.0005 for red galaxies with NUV-r>5.0. The average
molecular-to-atomic hydrogen ratio in present-day galaxies is 0.3, with
significant scatter from one galaxy to the next. The existence of strong
detection thresholds in both the HI and CO lines suggests that "quenching"
processes have occurred in these systems. Intriguingly, atomic gas strongly
dominates in the minority of galaxies with significant cold gas that lie above
these thresholds. This suggests that some re-accretion of gas may still be
possible following the quenching event.Comment: Accepted for publications in MNRAS. 32 pages, 25 figure
COLD GASS, an IRAM Legacy Survey of Molecular Gas in Massive Galaxies: II. The non-universality of the Molecular Gas Depletion Timescale
We study the relation between molecular gas and star formation in a
volume-limited sample of 222 galaxies from the COLD GASS survey, with
measurements of the CO(1-0) line from the IRAM 30m telescope. The galaxies are
at redshifts 0.025<z<0.05 and have stellar masses in the range
10.0<log(M*/Msun)<11.5. The IRAM measurements are complemented by deep Arecibo
HI observations and homogeneous SDSS and GALEX photometry. A reference sample
that includes both UV and far-IR data is used to calibrate our estimates of
star formation rates from the seven optical/UV bands. The mean molecular gas
depletion timescale, tdep(H2), for all the galaxies in our sample is 1 Gyr,
however tdep(H2) increases by a factor of 6 from a value of ~0.5 Gyr for
galaxies with stellar masses of 10^10 Msun to ~3 Gyr for galaxies with masses
of a few times 10^11 Msun. In contrast, the atomic gas depletion timescale
remains contant at a value of around 3 Gyr. This implies that in high mass
galaxies, molecular and atomic gas depletion timescales are comparable, but in
low mass galaxies, molecular gas is being consumed much more quickly than
atomic gas. The strongest dependences of tdep(H2) are on the stellar mass of
the galaxy (parameterized as log tdep(H2)= (0.36+/-0.07)(log M* -
10.70)+(9.03+/-0.99)), and on the specific star formation rate. A single
tdep(H2) versus sSFR relation is able to fit both "normal" star-forming
galaxies in our COLD GASS sample, as well as more extreme starburst galaxies
(LIRGs and ULIRGs), which have tdep(H2) < 10^8 yr. Normal galaxies at z=1-2 are
displaced with respect to the local galaxy population in the tdep(H2) versus
sSFR plane and have molecular gas depletion times that are a factor of 3-5
times longer at a given value of sSFR due to their significantly larger gas
fractions.Comment: Accepted for publication in MNRAS. 19 pages, 11 figure
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