THE EFFECT OF HALO MASS ON THE H I CONTENT OF GALAXIES IN GROUPS AND CLUSTERS

We combine data from the Sloan Digital Sky Survey (SDSS) and the Arecibo Legacy Fast ALFA Survey (ALFALFA) to study the cold atomic gas content of galaxies in groups and clusters in the local universe. A careful cross-matching of galaxies in the SDSS, ALFALFA, and SDSS group catalogs provides a sample of group galaxies with stellar masses 10(8.4)M(circle dot) <= M-* <= 10(10.6)M(circle dot) and group halo masses 10(12.5) h(-1) M-circle dot <= M-h <= 10(15.0)h(-1)M(circle dot) Controlling our sample in stellar mass and redshift, we find no significant radial variation in the galaxy H I gas-to-stellar mass ratio for the halo mass range in our sample. However, the fraction of galaxies detected in ALFALFA declines steadily toward the centers of groups, with the effect being most prominent in the most massive halos. In the outskirts of massive halos a hint of a depressed detection fraction for low-mass galaxies suggests pre-processing that decreases the H I in these galaxies before they fall into massive clusters. We interpret the decline in the ALFALFA detection of galaxies in the context of a threshold halo mass for ram pressure stripping for a given galaxy stellar mass. The lack of an observable decrease in the galaxy H I gas-to-stellar mass ratio with the position of galaxies within groups and clusters highlights the difficulty of detecting the impact of environment on the galaxy H I content in a shallow H I survey.