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 ( \langle W _ { r } ( 2796 ) \rangle = 0.65 \pm 0.13 Å ) and covering fraction ( f _ { c } = 0.89 _ { -0.09 } ^ { +0.05 } ) are larger than isolated absorbers ( 1.27 \sigma and 2.2 \sigma , 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 ( 0.8 \sigma ) , 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 ( 1.7 \sigma ) and velocity dispersions ( 2.5 \sigma ) 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 .