2023MNRAS.521.1113B

We examine to what extent disc and outflow models can reproduce observations of H I gas within a few virial radii of galaxies in pairs and groups. Using highly sensitive HST/COS and FOS spectra of the Q0107 quasar triplet covering Ly α for z≲1, as well as a deep galaxy redshift survey including VIMOS, DEIMOS, GMOS, and MUSE data, we test simple disc and outflow models against the H I absorption along three lines-of-sight (separated by 200-500 kpc) through nine galaxy groups in this field. These can be compared with our previous results in which these models can often be fit to the absorption around isolated galaxies. Our models can reproduce ≈ 75 per cent of the 28 identified absorption components within 500 km s^–1 of a group galaxy, so most of the H I around groups is consistent with a superposition of the CGM of the individual galaxies. Gas stripped in interactions between galaxies may be a plausible explanation for some of the remaining absorption, but neither the galaxy images nor the galaxy and absorber kinematics provide clear evidence of such stripped material, and these unexplained absorbers do not preferentially occur around close pairs of galaxies. We find H I column densities typically higher than at similar impact parameters around isolated galaxies (≈ 2.5σ), as well as more frequent detections of O VI than around isolated galaxies (30 per cent of sightlines to 7 per cent).