The High-Ion Content and Kinematics of Low-Redshift Lyman Limit Systems

We study the high-ion content and kinematics of the circumgalactic medium around low-redshift galaxies using a sample of 23 Lyman limit systems (LLSs) at 0.08 < z < 0.93 observed with the Cosmic Origins Spectrograph on board the Hubble Space Telescope . In Lehner et al., we recently showed that low- z LLSs have a bimodal metallicity distribution. Here we extend that analysis to search for differences between the high-ion and kinematic properties of the metal-poor and metal-rich branches. We find that metal-rich LLSs tend to show higher O vi columns and broader O vi profiles than metal-poor LLSs. The total H i line width (Δ v 90 statistic) in LLSs is not correlated with metallicity, indicating that the H i kinematics alone cannot be used to distinguish inflow from outflow and gas recycling. Among the 17 LLSs with O vi detections, all but two show evidence of kinematic sub-structure, in the form of O vi –H i centroid offsets, multiple components, or both. Using various scenarios for how the metallicities in the high-ion and low-ion phases of each LLS compare, we constrain the ionized hydrogen column in the O vi phase to lie in the range log N (H ii ) ∼ 17.6–20. The O vi phase of LLSs is a substantial baryon reservoir, with M (high-ion) ∼ 10 8.5–10.9 ( r /150 kpc) 2 M ☉ , similar to the mass in the low-ion phase. Accounting for the O vi phase approximately doubles the contribution of low- z LLSs to the cosmic baryon budget.