The Red Dead Redemption Survey of Circumgalactic Gas about Massive Galaxies. I. Mass and Metallicity of the Cool Phase

Abstract

We present a search for H I in the circumgalactic medium (CGM) of 21 massive (< {log}{M}_\star > ∼ 11.4), luminous red galaxies (LRGs) at z ∼ 0.5. Using UV spectroscopy of QSO sightlines projected within 500 kpc (∼{R}_vir}) of these galaxies, we detect H I absorption in 11/21 sightlines, including two partial Lyman limit systems and two Lyman limit systems. The covering factor of {log}N({{H}} {{I}})≥slant 16.0 gas within the virial radius of these LRGs is {f}_c(ρ ≤slant {R}_vir})={0.27}_-0.10^+0.11, while for optically thick gas ({log}N({{H}} {{I}})≥slant 17.2) it is {f}_c(ρ ≤slant {R}_vir})={0.15}_-0.07^+0.10. Combining this sample of massive galaxies with previous galaxy-selected CGM studies, we find no strong dependence of the H I covering factor on galaxy mass, although star-forming galaxies show marginally higher covering factors. There is no evidence for a critical mass above which dense, cold (T ∼ 10⁴ K) gas is suppressed in the CGM of galaxies (spanning stellar masses 9.5≲ {log}{M}_\star ≲ 11.8). The metallicity distribution in LRGs is indistinguishable from those found about lower-mass star-forming galaxies, and we find low-metallicity gas with [{{X}}/{{H}}]≈ -1.8 (1.5% solar) and below about massive galaxies. About half the cases show supersolar [Fe II/{Mg} {{II}}] abundances as seen previously in cool gas near massive galaxies. While the high-metallicity cold gas seen in LRGs could plausibly result from condensation from a corona, the low-metallicity gas is inconsistent with this interpretation.