Kinematics of the O VI Circumgalactic Medium: Halo Mass Dependence and Outflow Signatures

Abstract

We probe the high-ionization circumgalactic medium by examining absorber kinematics, absorber-galaxy kinematics, and average absorption profiles of 31 O VI absorbers from the “Multiphase Galaxy Halos” Survey as a function of halo mass, redshift, inclination, and azimuthal angle. The galaxies are isolated at 0.12 < z _gal < 0.66 and are probed by a background quasar within D ≈ 200 kpc. Each absorber-galaxy pair has Hubble Space Telescope images and COS quasar spectra, and most galaxy redshifts have been accurately measured from Keck/ESI spectra. Using the pixel-velocity two-point correlation function (TPCF) method, we find that O VI absorber kinematics have a strong halo mass dependence. Absorbers hosted by ∼L* galaxies have the largest velocity dispersions, which we interpret to be that the halo virial temperature closely matches the temperature at which the collisionally ionized O VI fraction peaks. Lower-mass galaxies and group environments have smaller velocity dispersions. Total column densities follow the same behavior, consistent with theoretical findings. After normalizing out the observed mass dependence, we studied absorber-galaxy kinematics with a modified TPCF and found nonvirialized motions due to outflowing gas. Edge-on minor-axis gas has large optical depths concentrated near the galaxy systemic velocity as expected for bipolar outflows, while face-on minor-axis gas has a smoothly decreasing optical depth distribution out to large normalized absorber-galaxy velocities, suggestive of decelerating outflowing gas. Accreting gas signatures are not observed owing to “kinematic blurring,” in which multiple line-of-sight structures are observed. These results indicate that galaxy mass dominates O VI properties over baryon cycle processes.