Extreme circumgalactic HI and CIII absorption around the most massive,
  quenched galaxies
  Luminous red galaxies (LRGs) are the most massive galaxies at $z\sim 0.5$
and, by selection, have negligible star formation. These objects have halo
masses between those of $L_{*}$ galaxies, whose circumgalactic media (CGM) 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 (CIII 977) and HI lines in the CGM of two LRGs. The CIII lines have
equivalent widths of $\sim 1.8$ \r{A} and $\sim 1.2$ \r{A} , and velocity
spreads of $\sim 796$ km s$^{-1}$ and $\sim 1245$ km s$^{-1}$, exceeding all
such measurements from local $\sim L_{*}$ galaxies (maximal CIII equivalent
widths $\sim 1$ \r{A}). 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' CGM
originate from past activity (e.g., star formation or active galactic nuclei
driven outflows) or from the CGM of galaxies in overlapping subhalos. We favor
the latter scenario, in which the properties of the CGM are more tightly linked
to the underlying dark matter halo than properties of the targeted galaxies
(e.g., star formation).
