The GALEX Arecibo SDSS Survey - VIII. Final data release. The effect of group environment on the gas content of massive galaxies

We present the final data release from the GALEX Arecibo SDSS Survey (GASS), a large Arecibo programme that measured the HI properties for an unbiased sample of similar to 800 galaxies with stellar masses greater than 10(10) M-circle dot and redshifts 0.025 < z < 0.05. This release includes new Arecibo observations for 250 galaxies. We use the full GASS sample to investigate environmental effects on the cold gas content of massive galaxies at fixed stellar mass. The environment is characterized in terms of dark matter halo mass, obtained by cross-matching our sample with the Sloan Digital Sky Survey (SDSS) group catalogue of Yang et al. Our analysis provides, for the first time, clear statistical evidence that massive galaxies located in haloes with masses of 10(13) - 10(14) M-circle dot have at least 0.4 dex less HI than objects in lower density environments. The process responsible for the suppression of gas in group galaxies most likely drives the observed quenching of the star formation in these systems. Our findings strongly support the importance of the group environment for galaxy evolution, and have profound implications for semi-analytic models of galaxy formation, which currently do not allow for stripping of the cold interstellar medium in galaxy groups.