Circumgalactic Medium at High Halo Masses—Signatures of Cold Gas Depletion in Luminous Red Galaxies

Abstract

We study ultraviolet H i and metal-line transitions in the circumgalactic medium (CGM) of 15 massive, quenched luminous red galaxies (LRGs) at redshift z ∼ 0.5 and with impact parameters up to 400 kpc. We selected eight LRG–CGM systems to study general properties of the CGM around LRGs, while the other seven are already known to contain cool CGM gas from Mg ii optical studies (Mg ii-LRGs). In the general LRG population, we detect H i in four of eight LRGs, in all cases with N H I < 1016.7cm−2. In contrast, all Mg ii-LRGs show H i; for four LRGs, the H i column density is N H I ≳ 1018cm−2. The CGM of LRGs also shows low and intermediate ionized lines (such as C iii, C ii, Si iii, and Si ii) and highly ionized lines of O vi (we detect O vi around five of seven Mg ii-LRGs and one of eight in the random sample). Next, we combine our sample with literature LRGs and ≲L * galaxies, and we find that while for ≲L * galaxies CGM H i Lyα absorption is stronger as galaxies are more massive, the cool CGM traced by H i Lyα is suppressed above stellar masses of M* ∼ 1011.5 M ☉. While most LRG–CGM systems show weak or nondetectable O vi (equivalent width < 0.2 Å), a few LRG–CGM systems show strong O vi 1031, which in most cases likely originates from groups containing both an LRG and a blue star-forming neighboring galaxy.