HALO MASS DEPENDENCE OF H i AND O vi ABSORPTION: EVIDENCE FOR DIFFERENTIAL KINEMATICS

We studied a sample of 14 galaxies (0.1 < z < 0.7) using HST/WFPC2 imaging and high-resolution HST/COS or HST/STIS quasar spectroscopy of Lyα, Lyβ, and O vi λλ1031, 1037 absorption. The galaxies, having 10.8 ⩽ log (M h/M☉) ⩽ 12.2, lie within D = 300 kpc of quasar sightlines, probing out to D/Rvir = 3. When the full range of M h and D/Rvir of the sample are examined, ∼40% of the H i absorbing clouds can be inferred to be escaping their host halo. The fraction of bound clouds decreases as D/Rvir increases such that the escaping fraction is ∼15% for D/Rvir < 1, ∼45% for 1 ⩽ D/Rvir < 2, and ∼90% for 2 ⩽ D/Rvir < 3. Adopting the median mass log M h/M☉ = 11.5 to divide the sample into “higher” and “lower” mass galaxies, we find a mass dependency for the hot circumgalactic medium kinematics. To our survey limits, O vi absorption is found in only ∼40% of the H i clouds in and around lower mass halos as compared to ∼85% around higher mass halos. For D/Rvir < 1, lower mass halos have an escape fraction of ∼65%, whereas higher mass halos have an escape fraction of ∼5%. For 1 ⩽ D/Rvir < 2, the escape fractions are ∼55% and ∼35% for lower mass and higher mass halos, respectively. For 2 ⩽ D/Rvir < 3, the escape fraction for lower mass halos is ∼90%. We show that it is highly likely that the absorbing clouds reside within 4Rvir of their host galaxies and that the kinematics are dominated by outflows. Our finding of “differential kinematics” is consistent with the scenario of “differential wind recycling” proposed by Oppenheimer et al. We discuss the implications for galaxy evolution, the stellar to halo mass function, and the mass–metallicity relationship of galaxies.