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 Hi line width (Delta v(90) statistic) in LLSs is not correlated with metallicity, indicating that the Hi kinematics alone cannot be used to distinguish inflow from outflow and gas recycling. Among the 17 LLSs with Ovi detections, all but two show evidence of kinematic sub-structure, in the form of O VI-HI 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) similar to 17.6-20. The O VI phase of LLSs is a substantial baryon reservoir, with M(high-ion) similar to 10(8.5-10.9) (r/150 kpc)(2) M-circle dot, similar to the mass in the low-ion phase. Accounting for the Ovi phase approximately doubles the contribution of low-z LLSs to the cosmic baryon budget.