The COS CGM Compendium (CCC). II. Lyman limit syst.

We focus here on 82 partial Lyman limit systems (pLLSs, 16.2<=logN_HI_<17.2) and 29 LLSs (17.2<=logN_HI_<19). Using Bayesian techniques and Markov Chain Monte Carlo sampling of a grid of photoionization models, we derive the posterior probability distribution functions (PDFs) for the metallicity of each absorber in CCC.

We show that the combined pLLS metallicity PDF at z<~1 has two main peaks at [X/H]~-1.7 and -0.4, with a strong dip at [X/H]~-1. The metallicity PDF of the LLSs might be more complicated than a unimodal or bimodal distribution. The pLLSs and LLSs probe a similar range of metallicities -3<~[X/H]<~+0.4, but the fraction of very metal-poor absorbers with [X/H]<~-1.4 is much larger for the pLLSs than the LLSs.