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

We present a search for H I in the circumgalactic medium (CGM) of 21 massive (< log M-*> similar to 11.4), luminous red galaxies (LRGs) at z similar to 0.5. Using UV spectroscopy of QSO sightlines projected within 500 kpc (similar to 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) >= 16.0 gas within the virial radius of these LRGs is f(c) (rho <= R-vir) = 0.271(-0.10)(+0.11), while for optically thick gas (log N(H I) >= 17.2) it is f(c)(rho <= 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 similar to 10(4) K) gas is suppressed in the CGM of galaxies (spanning stellar masses 9.5 less than or similar to log M-* less than or similar to 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] approximate to -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.