The atomic hydrogen content of galaxies as a function of group-centric radius

Abstract

\n We apply a spectral stacking technique to Westerbork Synthesis Radio Telescope observations to measure the neutral atomic hydrogen content (H\u2009i) of nearby galaxies in and around galaxy groups at z < 0.11. Our sample includes 577 optically selected galaxies (120 isolated galaxies and 457 satellites) covering stellar masses between 1010 and 1011.5 M⊙, cross-matched with Yang’s group catalogue, with angular and redshift positions from the Sloan Digital Sky Survey. We find that the satellites in the centres of groups have lower H\u2009i masses at fixed stellar mass and morphology (characterized by the inverse concentration index) relative to those at larger radii. These trends persist for satellites in both high-mass ($M_{\\rm halo} \\gt 10^{13.5}\\, h^{-1}\\, \\mathrm{M}_{\\odot }$) and low-mass ($M_{\\rm halo} \\leqslant 10^{13.5}\\, h^{-1}\\, \\mathrm{M}_{\\odot }$) groups, but disappear if we only consider group members in low local density (Σ < 5 gal\u2009Mpc−2) environments. Similar trends are found for the specific star formation rate. Interestingly, we find that the radial trends of decreasing H\u2009i mass with decreasing group-centric radius extend beyond the group virial radius, as isolated galaxies close to larger groups lack H\u2009i compared with those located more than ∼3.0 R180 away from the centre of their nearest group. We also measure these trends in the late-type subsample and obtain similar results. Our results suggest that the H\u2009i reservoir of galaxies can be affected before galaxies become group satellites, indicating the existence of pre-processing in the infalling isolated galaxies.