On the possible environmental effect in distributing heavy elements beyond individual gaseous haloes

Abstract

We present a study of extended galaxy halo gas through H I and O VI absorption over two decades in projected distance at z ≈ 0.2. The study is based on a sample of 95 galaxies from a highly complete (>80 per cent) survey of faint galaxies (L > 0.1L_*) with archival quasar absorption spectra and 53 galaxies from the literature. A clear anticorrelation is found between H I (O VI) column density and virial radius normalized projected distance, d/R_h. Strong H I (O VI) absorption systems with column densities greater than 10^14.0 (10^13.5) cm^-2 are found for 48 of 54 (36 of 42) galaxies at d < R_h indicating a mean covering fraction of < κ_{H I} > = 0.89 (< κ_{O VI} > = 0.86). O VI absorbers are found at d ≈ R_h, beyond the extent observed for lower ionization species. At d/R_h = 1-3 strong H I (O VI) absorption systems are found for only 7 of 43 (5 of 34) galaxies (< κ_{H I} > = 0.16 and < κ_{O VI} > = 0.15). Beyond d = 3 R_h, the H I and O VI covering fractions decrease to levels consistent with coincidental systems. The high completeness of the galaxy survey enables an investigation of environmental dependence of extended gas properties. Galaxies with nearby neighbours exhibit a modest increase in O VI covering fraction at d > R_h compared to isolated galaxies (κ_{O VI}≈ 0.13 versus 0.04) but no excess H I absorption. These findings suggest that environmental effects play a role in distributing heavy elements beyond the enriched gaseous haloes of individual galaxies. Finally, we find that differential H I and O VI absorption between early- and late-type galaxies continues from d < R_h to d ≈ 3 R_h.