2018MNRAS.479.2547C

We present a new Hubble Space Telescope Cosmic Origins Spectrograph (COS) absorption-line survey to study halo gas around 16 luminous red galaxies (LRGs) at z = 0.21-0.55. The LRGs are selected uniformly with stellar mass M_ star_>1011^M_☉ and no prior knowledge of the presence/absence of any absorption features. Based on observations of the full Lyman series, we obtain accurate measurements of neutral hydrogen column density N( H I) and find that high-N( H I) gas is common in these massive quiescent haloes with a median of <logN( H I)>= 16.6 at projected distances d <= 160 kpc. We measure a mean covering fraction of optically thick gas with logN( H I)≳17.2 of <κ>_ LLS_=0.44+0.12^_–0.11 at d <= 160 kpc and <κ>_ LLS_=0.71+0.11^_–0.20 at d <= 100 kpc. The line-of-sight velocity separations between the H I absorbing gas and LRGs are characterized by a mean and dispersion of <v_ gas- gal_>=29 km s^–1 and σ_<v_ gas- gal>_=171 km s^–1. Combining COS far-ultraviolet and ground-based echelle spectra provides an expanded spectral coverage for multiple ionic transitions, from low-ionization MgII and Si II, to intermediate-ionization SiIII and C III, and to high-ionization O VI absorption lines. We find that intermediate ions probed by C III and Si III are the most prominent UV metal lines in LRG haloes with a mean covering fraction of <κ( CIII)>_0.1=0.75^+0.08_–0.13 for W_r(977) 0.1 Å at d < 160 kpc, comparable to what is seen for C III in L_* and sub-L_* star-forming and red galaxies but exceeding Mg II or O VI in quiescent halos. The COS-LRG survey shows that massive quiescent haloes contain widespread chemically enriched cool gas and that little distinction between LRG and star-forming haloes is found in their HI and C III content.