232 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
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
xGASS: gas-rich central galaxies in small groups and their connections to cosmic web gas feeding
We use deep H I observations obtained as part of the extended GALEX Arecibo SDSS survey (xGASS) to study the cold gas properties of central galaxies across environments. We find that below stellar masses of 1010.2 M⊙, central galaxies in groups have an average atomic hydrogen gas fraction ∼0.3 dex higher than those in isolation at the same stellar mass. At these stellar masses, group central galaxies are usually found in small groups of N = 2 members. The higher H I content in these low-mass group central galaxies is mirrored by their higher average star formation activity and molecular hydrogen content. At larger stellar masses, this difference disappears and central galaxies in groups have similar (or even smaller) gas reservoirs and star formation activity compared to those in isolation. We discuss possible scenarios able to explain our findings and suggest that the higher gas content in low-mass group central galaxies is likely due to the contributions from the cosmic web or H I-rich minor mergers, which also fuel their enhanced star formation activity
The GALEX Arecibo SDSS Survey. VI. Second Data Release and Updated Gas Fraction Scaling Relations
We present the second data release from the GALEX Arecibo SDSS Survey (GASS),
an ongoing large Arecibo program to measure the HI properties for an unbiased
sample of ~1000 galaxies with stellar masses greater than 10^10 Msun and
redshifts 0.025<z<0.05. GASS targets are selected from the Sloan Digital Sky
Survey (SDSS) spectroscopic and Galaxy Evolution Explorer (GALEX) imaging
surveys, and are observed until detected or until a gas mass fraction limit of
a few per cent is reached. This second data installment includes new Arecibo
observations of 240 galaxies, and marks the 50% of the complete survey. We
present catalogs of the HI, optical and ultraviolet parameters for these
galaxies, and their HI-line profiles. Having more than doubled the size of the
sample since the first data release, we also revisit the main scaling relations
of the HI mass fraction with galaxy stellar mass, stellar mass surface density,
concentration index, and NUV-r color, as well as the gas fraction plane
introduced in our earlier work.Comment: 30 pages, 12 figures. Accepted for publication in A&A. Version with
complete Appendix A 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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