The COS CGM Compendium. II. Metallicities of the partial and Lyman limit systems at z<=1. (2019)
Keywords :
cosmology observations ; galaxies: abundances ; galaxies: evolution ; galaxies: halos ; intergalactic medium ; quasars: absorption lines
Abstract:We present the results from our COS circumgalactic medium (CGM) compendium (CCC), a survey of the CGM at z<~1 using HI-selected absorbers with 15<logN_HI_<19. 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
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In Paper I (Lehner+, 2018, J/ApJ/866/33), we assembled a sample of 224
HI-selected absorbers with 15<logN_HI_<19 at z<~1. The data were
retrieved from the HST/COS G130M and/or G160M archive with
supplementary ground-based observations of MgII and FeII with
high-resolution Keck/HIRES and VLT/UVES spectra. An additional 39
absorbers are available from our two first surveys (Lehner+, 2013,
J/ApJ/770/138 and Wotta+ 2016ApJ...831...95W). Most of these extra
absorbers were observed with HST/STIS, FUSE, and HST/COS G140L.
In this paper, we focus solely on the partial Lyman limit systems
(pLLSs) and LLSs.
As part of our survey, we acquired new high-resolution observations of
MgII (and FeII; see Paper I) for 113 absorbers. Data for three of
these absorbers were also initially obtained with low-resolution
spectra (R~4000).
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