The COS CGM Compendium. V. The Dichotomy of O vi Associated with Low- and High-metallicity Cool Gas at z < 1

Abstract

We analyze the O vi content and kinematics for 126 H i -selected absorbers at 0.14 ≲ z ≲ 0.73 for which the metallicities of their cool photoionized phase have been determined. We separate the absorbers into 100 strong Ly α forest systems (SLFSs with 15 ≲ log N (H i ) −1.4) SLFSs, with 20% and 60% detection rates, respectively. The O vi detection frequency for the HM and LM pLLSs is, however, similar at ∼60%. The SLFSs and pLLSs without detected O vi are consistent with the absorbing gas being in a single phase, while those with O vi trace multiphase gas. We show that the O vi velocity widths and column densities have different distributions in LM and HM gas. We find a strong correlation between O vi column density and metallicity. The strongest ( $\mathrm{log}N$ (O vi ) ≳ 14) and broadest O vi absorbers are nearly always associated with HM absorbers, while weaker O vi absorbers are found in both LM and HM absorbers. From comparisons with galaxy-selected and blind O vi surveys, we conclude absorbers with $\mathrm{log}N$ (O vi ) ≳ 14 most likely arise in the CGM of star-forming galaxies. Absorbers with weak O vi likely trace the extended CGM or intergalactic medium, while those without O vi likely originate in the intergalactic medium.

Keywords

• Circumgalactic medium
• Quasar absorption line spectroscopy
• Galaxies