Extreme circumgalactic HI and CIII absorption around the most massive, quenched galaxies

Understand

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}).