The COS CGM Compendium. III: Metallicity and Physical Properties of the Cool Circumgalactic Medium at z<1. (arXiv:1902.10147v1 [astro-ph.GA]) <a href="http://arxiv.org/find/astro-ph/1/au:+Lehner_N/0/1/0/all/0/1">Nicolas Lehner</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wotta_C/0/1/0/all/0/1">Christopher B. Wotta</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Howk_J/0/1/0/all/0/1">J. Christopher Howk</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+OMeara_J/0/1/0/all/0/1">John M. O'Meara</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Oppenheimer_B/0/1/0/all/0/1">Benjamin D. Oppenheimer</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cooksey_K/0/1/0/all/0/1">Kathy L. Cooksey</a>
We characterize the metallicities and physical properties of cool, We characterize the metallicities and physical properties of cool, http://arxiv.org/icons/sfx.gif
photoionized gas in a sample of 152 z<1 strong Ly$alpha$ forest systems
(SLFSs, absorbers with 15
photoionized gas in a sample of 152 z<1 strong Ly$alpha$ forest systems
(SLFSs, absorbers with 15<log N(HI)< 16.2). They are drawn from our COS
circumgalactic medium (CGM) compendium (CCC), an ultraviolet survey of
HI-selected circumgalactic gas around z<1 galaxies. We compare the metallicity
distribution of the SLFSs with the CCC results for 82 partial Lyman limit
systems (pLLSs, 16.2<log N(HI)<17.2) and 29 LLSs (17.2<log N(HI)<19). We show
that the metallicity probability distribution function (PDF) of the SLFSs at z<
1 is unimodal, skewed to low metallicities with a mean and median of [X/H] =
-1.44 and -1.16 dex, respectively. Very metal-poor gas (below those found in
z<1 damped Ly$alpha$ absorbers, [X/H]<-1.4) represents about half of the
population in both SLFSs and pLLSs. Thus there are important reservoirs of
primitive (though not pristine) gas around z< 1 galaxies. The photoionized gas
around z<1 galaxies is highly inhomogeneous based on the wide range of
metallicities observed (-3<[X/H]<+0.4) and large metallicity variations (factor
~2 to 20) of the closely redshift-spaced absorbers along the same sightlines.
With the unprecedentedly large sample of systems in CCC, we identify and
discuss some subtle cosmic evolution effects in the metallicities and
metallicity PDFs of these absorbers, which show a complex evolution with
redshift and HI column density. We compare our empirical results to recent
cosmological zoom simulations and explore the origins of the absorbers within
the EAGLE high-resolution simulations.
