The Properties of the Circumgalactic Medium in Red and Blue Galaxies: Results from the COS-GASS+COS-Halos Surveys
, , , , , , , , , and .
(2016)cite arxiv:1609.06308Comment: 18 pages, 18 figures, 2 tables. Accepted for publication in ApJ.

We use the combined data from the COS-GASS and COS-Halos surveys to characterize the Circum-Galactic Medium (CGM) surrounding typical low-redshift galaxies in the mass range $\rm~M_*\sim~10^9.5-11.5~M_ødot $, and over a range of impact parameters extending to just beyond the halo virial radius ($\rm~R_vir$). We find the radial scale length of the distributions of the equivalent widths of the Lyman~$\alpha$ and Si III absorbers to be 0.9 and 0.4 $\rm~R_vir$, respectively. The radial distribution of equivalent widths is relatively uniform for the blue galaxies, but highly patchy (low covering fraction) for the red galaxies. We also find that the Lyman~$\alpha$ and Si III equivalent widths show significant positive correlations with the specific star-formation rate (sSFR) of the galaxy. We find a surprising lack of correlations between the halo mass (virial velocity) and either the velocity dispersions or velocity offsets of the Lyman~$\alpha$ lines. The ratio of the velocity offset to the velocity dispersion for the Lyman~$\alpha$ absorbers has a mean value of $\sim$ 4, suggesting that a given the line-of-sight is intersecting a dynamically coherent structure in the CGM rather than a sea of orbiting clouds. The kinematic properties of the CGM are similar in the blue and red galaxies, although we find that a significantly larger fraction of the blue galaxies have large Lyman~$\alpha$ velocity offsets (>200 km s$^-1$). We show that - if the CGM clouds represent future fuel for star-formation - our new results could imply a large drop in the specific star-formation rate across the galaxy mass-range we probe.
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