1,187 research outputs found
The GALEX Arecibo SDSS Survey VII: The Bivariate Neutral Hydrogen-Stellar Mass Function for Massive Galaxies
We present the bivariate neutral atomic hydrogen (HI)---stellar mass function
(HISMF) (phi(M_HI, M_*)) for massive (log M_*/M_sun > 10) galaxies derived from
a sample of 480 local (0.025 < z < 0.050) galaxies observed in HI at Arecibo as
part of the GALEX Arecibo SDSS Survey (GASS). We fit six different models to
the HISMF and find that a Schechter function that extends down to a 1% HI gas
fraction, with an additional fractional contribution below that limit, is the
best parametrization of the HISMF. We calculate Omega_{HI, M_* >10^10} and find
that massive galaxies contribute 41% of the HI density in the local universe.
In addition to the binned HISMF we derive a continuous bivariate fit, which
reveals that the Schechter parameters only vary weakly with stellar mass:
M_HI^*, the characteristic HI mass, scales as M_*^0.39, alpha, the slope of the
HISMF at moderate HI masses, scales as M_*^0.07, and f, the fraction of
galaxies with HI gas fraction greater than 1%, scales as M_*^-0.24. The
variation of f with stellar mass should be a strong constraint for numerical
simulations. To understand the physical mechanisms that produce the shape of
the HISMF we redefine the parameters of the Schechter function as explicit
functions of stellar mass and star formation rate to produce a trivariate fit.
This analysis reveals strong trends with SFR. While M_HI^* varies weakly with
stellar mass and SFR, alpha is a stronger function of both stellar mass and
especially star formation rate. The HISMF is a crucial tool that can be used to
constrain cosmological galaxy simulations, test observational predictions of
the HI content of populations of galaxies, and identify galaxies whose
properties deviate from average trends.Comment: 31 pages, 20 figures, accepted to Ap
Evolution of the Stellar Mass--Metallicity Relation - I: Galaxies in the z~0.4 Cluster Cl0024
We present the stellar mass-stellar metallicity relationship (MZR) in the
Cl0024+1654 galaxy cluster at z~0.4 using full spectrum stellar population
synthesis modeling of individual quiescent galaxies. The lower limit of our
stellar mass range is , the lowest galaxy mass at which
individual stellar metallicity has been measured beyond the local universe. We
report a detection of an evolution of the stellar MZR with observed redshift at
dex per Gyr, consistent with the predictions from
hydrodynamical simulations. Additionally, we find that the evolution of the
stellar MZR with observed redshift can be explained by an evolution of the
stellar MZR with their formation time, i.e., when the single stellar population
(SSP)-equivalent ages of galaxies are taken into account. This behavior is
consistent with stars forming out of gas that also has an MZR with a
normalization that decreases with redshift. Lastly, we find that over the
observed mass range, the MZR can be described by a linear function with a
shallow slope, (). The slope suggests
that galaxy feedback, in terms of mass-loading factor, might be
mass-independent over the observed mass and redshift range.Comment: 22 pages, 10 figures. Accepted for publication in Ap
The Dynamical Distinction between Elliptical and Lenticular Galaxies in Distant Clusters: Further Evidence for the Recent Origin of S0 Galaxies
We examine resolved spectroscopic data obtained with the Keck II telescope
for 44 spheroidal galaxies in the fields of two rich clusters, Cl0024+16
(z=0.40) and MS0451-03 (z=0.54), and contrast this with similar data for 23
galaxies within the redshift interval 0.3<z<0.65 in the GOODS northern field.
For each galaxy we examine the case for systemic rotation, derive central
stellar velocity dispersions sigma and photometric ellipticities, epsilon.
Using morphological classifications obtained via Hubble Space Telescope imaging
as the basis, we explore the utility of our kinematic quantities in
distinguishing between pressure-supported ellipticals and
rotationally-supported lenticulars (S0s). We demonstrate the reliability of
using the v/(1-epsilon) vs sigma and v/sigma vs epsilon distributions as
discriminators, finding that the two criteria correctly identify 63%+-3% and
80%+-2% of S0s at z~0.5, respectively, along with 76%+8-3% and 79%+-2% of
ellipticals. We test these diagnostics using equivalent local data in the Coma
cluster, and find that the diagnostics are similarly accurate at z=0. Our
measured accuracies are comparable to the accuracy of visual classification of
morphologies, but avoid the band-shifting and surface brightness effects that
hinder visual classification at high redshifts. As an example application of
our kinematic discriminators, we then examine the morphology-density relation
for elliptical and S0 galaxies separately at z~0.5. We confirm, from kinematic
data alone, the recent growth of rotationally-supported spheroidals. We discuss
the feasibility of extending the method to a more comprehensive study of
cluster and field galaxies to z~1, in order to verify in detail the recent
density-dependent growth of S0 galaxies.Comment: 7 pages, 4 figures, updated with version accepted to Ap
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
Structure of androcam supports specialized interactions with myosin VI
Androcam replaces calmodulin as a tissue-specific myosin VI light
chain on the actin cones that mediate D. melanogaster spermatid
individualization. We show that the androcam structure and its
binding to the myosin VI structural (Insert 2) and regulatory (IQ)
light chain sites are distinct from those of calmodulin and provide
a basis for specialized myosin VI function. The androcam N lobe
noncanonically binds a single Ca2ĂŸ and is locked in a âclosedâ conformation,
causing androcam to contact the Insert 2 site with its C
lobe only. Androcam replacing calmodulin at Insert 2 will increase
myosin VI lever arm flexibility, which may favor the compact monomeric
form of myosin VI that functions on the actin cones by facilitating
the collapse of the C-terminal region onto the motor
domain. The tethered androcam N lobe could stabilize the monomer
through contacts with C-terminal portions of the motor or
recruit other components to the actin cones. Androcam binds the
IQ site at all calcium levels, constitutively mimicking a conformation
adopted by calmodulin only at intermediate calcium levels. Thus,
androcam replacing calmodulin at IQ will abolish a Ca2ĂŸ-regulated,
calmodulin-mediated myosin VI structural change. We propose that
the N lobe prevents androcam from interfering with other calmodulin-
mediated Ca2ĂŸ signaling events. We discuss how gene duplication
and mutations that selectively stabilize one of the many conformations
available to calmodulin support the molecular evolution
of structurally and functionally distinct calmodulin-like proteins
Connection Between the Circumgalactic Medium and the Interstellar Medium of Galaxies: Results from the COS-GASS Survey
We present a study exploring the nature and properties of the Circum-Galactic
Medium (CGM) and its connection to the atomic gas content in the interstellar
medium (ISM) of galaxies as traced by the HI 21cm line. Our sample includes 45
low-z (0.026-0.049) galaxies from the GALEX Arecibo SDSS Survey. Their CGM was
probed via absorption in the spectra of background Quasi-Stellar Objects at
impact parameters of 63 to 231kpc. The spectra were obtained with the Cosmic
Origins Spectrograph aboard the Hubble Space Telescope. We detected neutral
hydrogen (Ly absorption-lines) in the CGM of 92% of the galaxies. We
find the radial profile of the CGM as traced by the Ly equivalent width
can be fit as an exponential with a scale length of roughly the virial radius
of the dark matter halo. We found no correlation between the orientation of
sightline relative to the galaxy major axis and the Ly equivalent
width. The velocity spread of the circumgalactic gas is consistent with that
seen in the atomic gas in the interstellar medium. We find a strong correlation
(99.8% confidence) between the gas fraction (M(HI)/M*) and the
impact-parameter-corrected Ly equivalent width. This is stronger than
the analogous correlation between corrected Ly equivalent width and
SFR/M* (97.5% confidence). These results imply a physical connection between
the HI disk and the CGM, which is on scales an order-of-magnitude larger. This
is consistent with the picture in which the HI disk is nourished by accretion
of gas from the CGM.Comment: 13 pages, 9 figures, and 2 tables. Submitted to Ap
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
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