  We use the Galaxies-Intergalactic Medium Interaction Calculation (GIMIC)
cosmological hydrodynamic simulation at z=0 to study the distribution and
environmental dependence of neutral hydrogen (HI) gas in the outskirts of
simulated galaxies. This gas can currently be probed directly in, for example,
Ly$\alpha$ absorption via the observation of background quasars. Radio
facilities, such as the Square Kilometre Array, will provide a complementary
probe of the diffuse HI in emission and will constrain the physics underpinning
the complex interplay between accretion and feedback mechanisms which affect
the intergalactic medium. We extract a sample of 488 galaxies from a
re-simulation of the average cosmic density GIMIC region. We estimate the
neutral hydrogen content of these galaxies and the surrounding intergalactic
medium within which they reside. We investigate the average HI radial profiles
by stacking the individual profiles according to both mass and environment. We
find high HI column densities at large impact parameters in group environments
and markedly lower HI densities for non-group galaxies. We suggest that these
results likely arise from the combined effects of ram pressure stripping and
tidal interactions present in group environments.

Cosmology and Nongalactic Astrophysics