Аннотация
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
HST. 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.
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