Kinematics of Circumgalactic O <scp>vi</scp> Gas and Disk Rotation of <i>z</i> ≈ 0.2 Star-forming Galaxies

Abstract Quasar sightline observations reveal that low ionization state gas corotates with the galaxy disk and often at subcentrifugal velocities, suggesting that the gas is spiraling toward the galaxy disk. However, while observations ubiquitously detect O vi absorption around low-redshift, ∼ L * star-forming galaxies, the relationship between O vi and the galaxy disk, especially the kinematics, is not well established. This work focuses on the O vi kinematics and its comparison with that of the low ions and galactic disk rotation. We present observations of 18 pairs of quasars and z ≈ 0.2 star-forming galaxies. All quasar sightlines intersect the circumgalactic medium (CGM) within 45° from the galaxy major axes. We show that while individual O vi velocity components do not correlate with disk rotation, the bulk of the O vi gas in individual sightlines rarely counterrotates. We then match O vi velocity components with those of low ions by minimizing the difference of their velocity centroids. The O vi velocity components with successful low-ion matches are typically found at small sightline impact parameters and are more likely to corotate with the disk. We suggest that the low-ion-matched O vi velocity components trace the gas cospatial with the low ions near the extended disk plane in the inner CGM, whereas those without low-ion matches represent the gas at large 3D radii. While the gas at large radii is theoretically expected to kinematically correlate with the disk angular momentum, this correlation is expected to be weaker due to the higher turbulent to mean rotation velocity ratio at large radii, consistent with our results.