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Centro de Astrofísica da Universidade do Porto

The GALEX Arecibo SDSS Survey. I. Gas Fraction Scaling Relations of Massive Galaxies and First Data Release

B. Catinella, D. Schiminovich, G. Kauffmann, S. Fabello, J. Wang, C. Hummels, J. Lemonias, S. M. Moran, R. Wu, R. Giovanelli, M. Haynes, T. Heckman, A. Basu-Zych, M. R. Blanton, J. Brinchmann, T. Budavári, T. Gonçalves, B. D. Johnson, R. C Kennicutt, B. F. Madore, C. D. Martin, M. R. Rich, L. Tacconi, D. A. Thilker, V. Wild, T. K. Wyder

Abstract
We introduce the GALEX Arecibo SDSS Survey (GASS), an on-going large program that is gathering high quality HI-line spectra using the Arecibo radio telescope for an unbiased sample of ∼1000 galaxies with stellar masses greater than 1010 M and redshifts 0.025 < z < 0.05, selected from the SDSS spectroscopic and Galaxy Evolution Explorer (GALEX) imaging surveys. The galaxies are observed until detected or until a low gas mass fraction limit (1.5-5 per cent) is reached. This paper presents the first Data Release, consisting of ∼20 per cent 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. A large fraction (∼60 per cent) of the galaxies in our sample are detected in HI. Even at stellar masses above 1011 M, the detected fraction does not fall below ∼40 per cent. We find that the atomic gas fraction MHI/M decreases strongly with stellar mass, stellar surface mass density and NUV-r colour, but is only weakly correlated with galaxy bulge-to-disk ratio (as measured by the concentration index of the r-band light). We also find that the fraction of galaxies with significant (more than a few per cent) HI decreases sharply above a characteristic stellar surface mass density of 108.5 M kpc-2. The fraction of gas-rich galaxies decreases much more smoothly with stellar mass. One of the key goals of the GASS survey is to identify and quantify the incidence of galaxies that are transitioning between the blue, star-forming cloud and the red sequence of passively evolving galaxies. Likely transition candidates can be identified as outliers from the mean scaling relations between MHI/M and other galaxy properties. We have fitted a plane to the two-dimensional relation between HI mass fraction, stellar surface mass 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.

Keywords
galaxies:evolution – galaxies: fundamental parameters – radio lines:galaxies - ultraviolet: galaxies

Monthly Notices of the Royal Astronomical Society
Volume 403, Page 683
February 2010

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