By comparing Mg II absorption in the circumgalactic medium (CGM) of group environments to isolated galaxies, we investigated the impact of environment on the CGM. A Mg II absorber is associated with a group if there are two or more galaxies at the absorption redshift within a projected distance of D = 200 kpc from a background quasar and a line-of-sight velocity separation of 500 km s −1 . We compiled a sample of 29 group environments consisting of 74 galaxies (2 − 5 galaxies per group) at 0.113 < z gal < 0.888. The group absorber median equivalent width ( W r (2796) = 0.65 ± 0.13 Å) and covering fraction ( f c = 0.89 +0.05 −0.09 ) are larger than isolated absorbers (1.27σ and 2.2σ, respectively) but median column densities are statistically consistent. A pixel-velocity two-point correlation function analysis shows that group environment kinematics are statistically comparable to isolated environments (0.8σ), but with more power for high velocity dispersions similar to outflow kinematics. Group absorbers display more optical depth at larger velocities. A superposition model in which multiple galaxies contribute to the observed gas matches larger equivalent width group absorbers, but overpredicts the kinematics significantly due to large velocity separations between member galaxies. Finally, galaxy-galaxy groups (similar member galaxy luminosities) may have larger absorber median equivalent widths (1.7σ) and velocity dispersions (2.5σ) than galaxy-dwarf groups (disparate luminosities). We suggest the observed gas is coupled to the group rather than individual galaxies, forming an intragroup medium. Gas may be deposited into this medium by multiple galaxies via outflowing winds undergoing an intergalactic transfer between member galaxies or from tidal stripping of interacting members.

We present a study comparing O VI λλ1031, 1037 doublet absorption found towards group galaxy environments with 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 to have two or more galaxies having 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 z gal = 0.1669 and a median impact parameter of D = 134.1 kpc. An additional 12 non-absorbing groups were identified with a median redshift of z gal = 0.2690 and a median impact parameter of D = 274.0 kpc. We find the average equivalent width to be smaller for group galaxies than for isolated galaxies (3σ). 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 (10σ). 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 ionised. The remaining O VI likely exists at the interface between hot, diffuse gas and cooler regions of the CGM.

We investigate the geometric distribution of gas metallicities in the circumgalactic medium (CGM) around 47, z<0.7 galaxies from the "Multiphase Galaxy Halos" Survey. Using a combination of quasar spectra from Hubble Space Telescope (HST)/COS and from Keck/HIRES or Very Large Telescope/UVES, we measure column densities of, or determine limits on, CGM absorption lines. We then use a Markov Chain Monte Carlo approach with Cloudy to estimate the metallicity of cool (T∼10 4 K) CGM gas. We also use HST images to determine hostgalaxy inclination and quasar-galaxy azimuthal angles. Our sample spans a H Icolumn density range of 13.8 cm −2 < N log H I <19.9 cm −2. We find (1) while the metallicity distribution appears bimodal, a Hartigan dip test cannot rule out a unimodal distribution (0.4σ). (2) CGM metallicities are independent of halo mass, spanning three orders of magnitude at a fixed halo mass. (3) The CGM metallicity does not depend on the galaxy azimuthal and inclination angles regardless of H Icolumn density, impact parameter, and galaxy color. (4) The ionization parameter does not depend on azimuthal angle. We suggest that the partial Lyman limit metallicity bimodality is not driven by a spatial azimuthal bimodality. Our results are consistent with simulations where the CGM is complex and outflowing, accreting, and recycled gas are well-homogenized at z<0.7. The presence of lowmetallicity gas at all orientations suggests that cold streams of accreting filaments are not necessarily aligned with the galaxy plane at low redshifts or intergalactic transfer may dominate. Finally, our results support simulations showing that strong metal absorption can mask the presence of low-metallicity gas in integrated line-of-sight CGM metallicities.