987 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
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
Evolution of the Stellar MassâMetallicity Relation. II. Constraints on Galactic Outflows from the Mg Abundances of Quiescent Galaxies
We present the stellar massâ[Fe/H] and massâ[Mg/H] relation of quiescent galaxies in two galaxy clusters at z ~ 0.39 and z ~ 0.54. We derive the age, [Fe/H], and [Mg/Fe] for each individual galaxy using a full-spectrum fitting technique. By comparing with the relations for z ~ 0 Sloan Digital Sky Survey galaxies, we confirm our previous finding that the massâ[Fe/H] relation evolves with redshift. The massâ[Fe/H] relation at higher redshift has lower normalization and possibly steeper slope. However, based on our sample, the massâ[Mg/H] relation does not evolve over the observed redshift range. We use a simple analytic chemical evolution model to constrain the average outflow that these galaxies experience over their lifetime, via the calculation of mass-loading factor. We find that the average mass-loading factor η is a power-law function of galaxy stellar mass, η â M*^(â0.21±0.09). The measured mass-loading factors are consistent with the results of other observational methods for outflow measurements and with the predictions where outflow is caused by star formation feedback in turbulent disks
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