708 research outputs found
HI and Star Formation Properties of Massive Galaxies: First Results from the GALEX Arecibo SDSS Survey
The GALEX Arecibo SDSS Survey (GASS) is an ambitious program designed to
investigate the cold gas properties of massive galaxies, a challenging
population for HI studies. Using the Arecibo radio telescope, GASS is gathering
high-quality HI-line spectra for an unbiased sample of ~1000 galaxies with
stellar masses greater than 10^10 Msun and redshifts 0.025 < z < 0.05,
uniformly selected from the SDSS spectroscopic and GALEX imaging surveys. The
galaxies are observed until detected or until a low gas mass fraction limit
(1.5-5%) is reached. We present initial results based on the first Data
Release, which consists of ~20% of the final GASS sample. We use this data set
to explore the main scaling relations of HI gas fraction with galaxy structure
and NUV-r colour, and show our best fit plane describing the relation between
gas fraction, stellar mass surface density and NUV-r colour. Interesting
outliers from this plane include gas-rich red sequence galaxies that may be in
the process of regrowing their disks, as well as blue, but gas-poor spirals.Comment: 4 pages, 2 figures. To appear in "Hunting for the Dark: The Hidden
Side of Galaxy Formation", Malta, 19-23 Oct. 2009, eds. V.P. Debattista &
C.C. Popescu, AIP Conf. Se
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
Implementazione software del codificatore e decodificatore turbo impiegati nello standard DVB-SH
Descrizione dello standard DVB-SH e implementazione software del codificatore e decodificatore impiegati.
Description of DVB-SH standard and software implementation of coder and decoder used
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
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