The High-Ion Content and Kinematics of Low-Redshift Lyman Limit Systems
  We study the high-ionization phase 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 onboard the
Hubble Space Telescope. In Lehner et al. (2013), 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 (dv90 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
metallicity 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 solar masses, 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.
