The COS CGM Compendium. II. Metallicities of the Partial and Lyman Limit Systems at z ≲ 1

We present the results from our COS circumgalactic medium (CGM) compendium (CCC), a survey of the CGM at z 19 have mostly -1<[X/H]<0 at z<1. The metal-enriched gas probed by pLLSs and LLSs confirms that galaxies that have been enriching their CGM over billions of years. Surprisingly, despite this enrichment, there is also abundant metal-poor CGM gas (41-59% of the pLLSs have [X/H]<-1.4), representing a reservoir of near-pristine gas around z<1 galaxies. We compare our empirical results to recent cosmological zoom simulations, finding some discrepancies, including an overabundance of metal-enriched CGM gas in simulations.