162 research outputs found
The GALEX Arecibo SDSS Survey (GASS)
The GALEX Arecibo SDSS Survey (GASS) is a large targeted survey that started
at Arecibo in March 2008. GASS is designed to measure the neutral hydrogen
content of ~1000 massive galaxies (with stellar mass Mstar > 10^10 Msun) at
redshift 0.025<z<0.05, uniformly selected from the SDSS spectroscopic and GALEX
imaging surveys. Our selected mass range straddles the recently identified
"transition mass" (Mstar ~3x10^10 Msun) above which galaxies show a marked
decrease in their present to past-averaged star formation rates. GASS will
produce the first statistically significant sample of massive "transition"
galaxies with homogeneously measured stellar masses, star formation rates and
gas properties. The analysis of this sample will allow us to investigate if and
how the cold gas responds to a variety of different physical conditions in the
galaxy, thus yielding insights on the physical processes responsible for the
transition between blue, star-forming and red, passively evolving galaxies.
GASS will be of considerably legacy value not only in isolation but also by
complementing ongoing HI-selected surveys.Comment: 3 pages, 2 figures. To appear in proceedings of "The Evolution of
Galaxies through the Neutral Hydrogen Window", R. Minchin & E. Momjian eds.
Higher resolution version at http://www.mpa-garching.mpg.de/GASS/pubs.ph
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
ALFALFA HI Data Stacking III. Comparison of environmental trends in HI gas mass fraction and specific star formation rate
It is well known that both the star formation rate and the cold gas content
of a galaxy depend on the local density out to distances of a few Megaparsecs.
In this paper, we compare the environmental density dependence of the atomic
gas mass fractions of nearby galaxies with the density dependence of their
central and global specific star formation rates. We stack HI line spectra
extracted from the Arecibo Legacy Fast ALFA survey centered on galaxies with UV
imaging from GALEX and optical imaging/spectroscopy from SDSS. We use these
stacked spectra to evaluate the mean atomic gas mass fraction of galaxies in
bins of stellar mass and local density. For galaxies with stellar masses less
than 10^10.5 M_sun, the decline in mean atomic gas mass fraction with density
is stronger than the decline in mean global and central specific star formation
rate. The same conclusion does not hold for more massive galaxies. We interpret
our results as evidence for ram-pressure stripping of atomic gas from the outer
disks of low mass satellite galaxies. We compare our results with the
semi-analytic recipes of Guo et al. (2011) implemented on the Millennium II
simulation. These models assume that only the diffuse gas surrounding satellite
galaxies is stripped, a process that is often termed "strangulation". We show
that these models predict relative trends in atomic gas and star formation that
are in disagreement with observations. We use mock catalogues generated from
the simulation to predict the halo masses of the HI-deficient galaxies in our
sample. We conclude that ram-pressure stripping is likely to become effective
in dark matter halos with masses greater than 10^13 M_sun.Comment: 12 pages, 10 figures. Accepted for publication in MNRA
Template Rotation Curves for Disk Galaxies
A homogeneous sample of ~2200 low redshift disk galaxies with both high
sensitivity long-slit optical spectroscopy and detailed I-band photometry is
used to construct average, or template, rotation curves in separate luminosity
classes, spanning 6 magnitudes in I-band luminosity. The template rotation
curves are expressed as functions both of exponential disk scale lengths r_d
and of optical radii Ropt, and extend out to 4.5-6.5 r_d, depending on the
luminosity bin. The two parameterizations yield slightly different results
beyond Ropt because galaxies whose Halpha emission can be traced to larger
extents in the disks are typically of higher optical surface brightness and are
characterized by larger values of Ropt/r_d. By either parameterization, these
template rotation curves show no convincing evidence of velocity decline within
the spatial scales over which they are sampled, even in the case of the most
luminous systems. In contrast to some previous expectations, the fastest
rotators (most luminous galaxies) have, on average, rotation curves that are
flat or mildly rising beyond the optical radius, implying that the dark matter
halo makes an important contribution to the kinematics also in these systems.
The template rotation curves and the derived functional fits provide
quantitative constraints for studies of the structure and evolution of disk
galaxies, which aim at reproducing the internal kinematics properties of disks
at the present cosmological epoch.Comment: 21 pages, 12 figures. To appear in the Astrophysical Journal (April
2006
Rotational Widths for Use in the Tully-Fisher Relation. II. The Impact of Surface Brightness
Using a large sample of spiral galaxies for which 21 cm single-dish and/or
long-slit optical spectra are available, we make a detailed comparison between
various estimates of rotational widths. Different optical width estimators are
considered and their limitations discussed, with emphasis on biases associated
with rotation curve properties (shape and extent) and disk central surface
brightness. The best match with HI rotational velocities is obtained with
Polyex widths, which are measured at the optical radius (encompassing a fixed
fraction of the total light of the galaxy) from a model fit to the rotation
curve. In contrast with Polyex widths, optical rotational velocities measured
at 2.15 disk scale lengths r_d deviate from HI widths by an amount that
correlates with the central surface brightness of the disk. This bias occurs
because the rotation curves of galaxies are in general still rising at 2.15
r_d, and the fraction of total mass contained within this radius decreases with
increasing disk surface brightness. Statistical corrections, parameterized by
the radial extent of the observed rotation curve, are provided to reduce Polyex
and HI width measurements into a homogeneous system. This yields a single
robust estimate of rotational velocity to be used for applications of disk
scaling relations.Comment: 13 pages, 8 figures. To appear in the Astronomical Journal (August
2007
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