The Impact of the Group Environment on the O vi Circumgalactic Medium

Abstract

We present a study comparing O vi λλ 1031, 1037 doublet absorption found toward group galaxy environments to that of isolated galaxies. The O vi absorption in the circumgalactic medium (CGM) of isolated galaxies has been studied previously by the “Multiphase Galaxy Halos” survey, where the kinematics and absorption properties of the CGM have been investigated. We extend these studies to group environments. We define a galaxy group as having two or more galaxies with a line-of-sight velocity difference of no more than 1000 km s −1 and located within 350 kpc (projected) of a background quasar sightline. We identified a total of six galaxy groups associated with O vi absorption W r > 0.06 Å that have a median redshift of and a median impact parameter of . An additional 12 non-absorbing groups were identified with a median redshift of and a median impact parameter of . We find the average equivalent width to be smaller for group galaxies than for isolated galaxies (3 σ ). However, the covering fractions are consistent with both samples. We used the pixel-velocity two-point correlation function method and find that the velocity spread of O vi in the CGM of group galaxies is significantly narrower than that of isolated galaxies (10 σ ). We suggest that the warm/hot CGM does not exist as a superposition of halos; instead, the virial temperature of the halo is hot enough for O vi to be further ionized. The remaining O vi likely exists at the interface between hot diffuse gas and cooler regions of the CGM.