238 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
Rotational Widths for Use in the Tully-Fisher Relation. I. Long-slit Spectroscopic Data
We present new long-slit Halpha spectroscopy for 403 non-interacting spiral
galaxies, obtained at the Palomar Observatory 5 m Hale telescope, which is used
to derive well-sampled optical rotation curves. Because many of the galaxies
show optical emission features which are significantly extended along the
spectrograph slit, a technique was devised to separate and subtract the night
sky lines from the galaxy emission. We exploit a functional fit to the rotation
curve to identify its center of symmetry; this method minimizes the asymmetry
in the final, folded rotation curve. We derive rotational widths using both
velocity histograms and the Polyex model fit. The final rotational width is
measured at a radius containing 83% of the total light as derived from I-band
images. In addition to presenting the new data, we use a large sample of 742
galaxies for which both optical long-slit and radio HI line spectroscopy are
available to investigate the relation between the HI content of the disks and
the extent of their rotation curves. Our results show that the correlation
between those quantities, which is well-established in the case of HI-poor
galaxies in clusters, is present also in HI-normal objects: for a given optical
size, star formation can be traced further out in the disks of galaxies with
larger HI mass.Comment: 16 pages, 6 figures. Full version of Table 1 and Figure 5 available
as separate files. To appear in AJ (September 2005
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