The Atomic Hydrogen Content of Galaxies as a function of Group-Centric
  Radius
  We apply a spectral stacking technique to Westerbork Synthesis Radio
Telescope observations to measure the neutral atomic hydrogen content (HI) 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 10$^{10}$ and 10$^{11.5}$ M$_{\odot}$,
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 HI masses at fixed stellar mass and morphology
(characterised by the inverse concentration index) relative to those at larger
radii. These trends persist for satellites in both high-mass ($M_{\rm halo} >
10^{13.5}h^{-1}$M$_{\odot}$) and low-mass ($M_{\rm halo} \leqslant
10^{13.5}h^{-1}$M$_{\odot}$) groups, but disappear if we only consider group
members in low local density ($\Sigma <$ 5 gal/Mpc$^{-2}$) environments.
Similar trends are found for the specific star formation rate. Interestingly,
we find that the radial trends of decreasing HI mass with decreasing
group-centric radius extend beyond the group virial radius, as isolated
galaxies close to larger groups lack HI compared with those located more than
$\sim$3.0 $R_{180}$ away from the center of their nearest group. We also
measure these trends in the late-type subsample and obtain similar results. Our
results suggest that the HI reservoir of galaxies can be affected before
galaxies become group satellites, indicating the existence of pre-processing in
the infalling isolated galaxies.
