Extreme Circumgalactic H I and C III Absorption around the Most Massive, Quenched Galaxies

Abstract

Luminous red galaxies (LRGs) are the most massive galaxies at z ∼ 0.5 and, by selection, have negligible star formation (SF). These objects have halo masses between those of L _* galaxies, whose circumgalactic media (CGMs) are observed to have large masses of cold gas, and clusters of galaxies, which primarily contain hot gas. Here, we report detections of strong and extended metal (C III 977) and H I lines in the CGM of two LRGs. The C III lines have equivalent widths (EWs) of ∼1.8 and ∼1.2 Å, and velocity spreads of ∼796 and ∼1245 {km} {{{s}}}^-1, exceeding all such measurements from local ∼L _* galaxies (maximal C III EWs ∼1 Å). The data demonstrate that a subset of halos hosting very massive, quenched galaxies contain significant complexes of cold gas. Possible scenarios to explain our observations include that the LRGs’ CGMs originate from past activity (e.g., SF or active galactic nuclei driven outflows) or from the CGMs of galaxies in overlapping subhalos. We favor the latter scenario, in which the properties of the CGMs are more tightly linked to the underlying dark matter halo than properties of the targeted galaxies (e.g., SF).