The COS CGM Compendium. V: the dichotomy in the properties of OVI associated with the low- and high-Metallicity HI-bearing gas

We analyze the OVI content and kinematics for 126 z < 1 HI-selected absorbers for which the metallicities of their cool photoionized phase have been determined. We separate the absorbers into 100 strong Lya forest systems (SLFSs with 15 ≲ logN(HI) < 16.2) and 26 partial Lyman Limit systems (pLLSs with 16.2 ≤ logN(HI) ≤ 17.2). The sample is drawn from the COS CGM Compendium (CCC) of Lehner et al. and has OVI coverage in S/N ≥ 8 HST/COS G130M/G160M QSO spectra, yielding a 2σ completeness level of logN(OVI) ≥ 13.6. There are significant differences in the OVI detection rates between low-metal (LM; [X/H] ≤ -1.4) SLFSs and high-metal (HM; [X/H] > -1.4) SLFSs, ∼15% versus ∼60 for the HM and LM pLLSs is, however, similar ∼60 with no OVI are consistent with gas being in a single-phase, while those with OVI trace multiphase gas. We find that the OVI velocity widths and column densities have different distributions in LM and HM gas. We observe a strong correlation between OVI column density and metallicity. The strongest (logN(OVI) ≳ 14) and broadest OVI absorbers are nearly systematically found to be associated with HM gas, while weaker OVI absorbers are found in both LM and HM HI-bearing gas. From comparisons with galaxy and OVI surveys, we conclude absorbers with logN(OVI) ≳ 14 most likely arise in the circumgalactic medium (CGM) of star-forming galaxies, with the broadest and strongest possibly tracing galaxy outflows. Absorbers with weak OVI most likely trace the extended CGM or intergalactic medium (IGM), while those without OVI in all likelihood originate in the IGM.