Observations show that spiral galaxies in galaxy clusters tend to have onaverage less neutral hydrogen (HI) than galaxies of the same type and size inthe field. There is accumulating evidence that such HI-deficient galaxies arealso relatively frequent in galaxy groups. An important question is, whichmechanisms are responsible for the gas deficiency in galaxy groups. To gain abetter understanding of how environment affects the gas content of galaxies, weidentified a sample of six HI-deficient galaxies from the HI Parkes All SkySurvey (HIPASS) using HI-optical scaling relations. One of the galaxies islocated in the outskirts of the Fornax cluster, four are in loose galaxy groupsand one is in a galaxy triplet. We present new high resolution HI observationswith the Australia Telescope Compact Array (ATCA) of these galaxies. We discussthe possible cause of HI-deficiency in these galaxies based on HI observationsand various multi-wavelength data. We find that the galaxies have truncated HIdisks, lopsided gas distribution and some show asymmetries in their stellardisks. We conclude that both ram pressure stripping and tidal interactions areimportant gas removal mechanisms in low density environments.

We characterize the physical properties of the cool T ~10^4 K circumgalacticmedium surrounding z ~2-3 quasar host galaxies, which are predicted to evolveinto present day massive ellipticals. Using a statistical sample of 14 quasarpairs with projected separation < 300 kpc and high dispersion, high S/Nspectra, we find extreme kinematics with low metal ion lines typically spanning~ 500 km/s, exceeding any previously studied galactic population. The CGM issignificantly enriched, even beyond the virial radius, with a medianmetallicity [M/H] ~ -0.6. The alpha/Fe abundance ratio is enhanced, suggestingthat halo gas is primarily enriched by core-collapse supernovae. The projectedcool gas mass within the virial radius is estimated to be 1.9*10^11 M_sun(R_\perp/160 kpc)^2, accounting for ~ 1/3 of the galaxy halo baryonic budget.The ionization state of CGM gas increases with projected distance from theforeground quasars, contrary to expectation if the quasar dominates theionizing radiation flux. However, we also found peculiarities not exhibited inthe CGM of other galaxy populations. In one absorption system, we may bedetecting unresolved fluorescent Ly-alpha emission, and another system showsstrong NV lines. Taken together these anomalies suggest that transversesightlines are at least in some cases possibly illuminated. We also discovereda peculiar case where detection of the CII* fine structure line implies anelectron density > 100 cm^-3 and subparsec scale gas clumps.