The Properties of the Circumgalactic Medium in Red and Blue Galaxies: Results from the COS-GASS+COS-Halos Surveys

TL;DR

This study analyzes the properties and kinematics of the circumgalactic medium in low-redshift galaxies using COS-GASS and COS-Halos data, revealing differences between red and blue galaxies and correlations with star formation activity.

Contribution

It provides new insights into the radial distribution, covering fraction, and kinematic behavior of the CGM in relation to galaxy color and star formation, using combined survey data.

Findings

Radial scale lengths of Lyman α and Si III absorbers are 0.9 and 0.4 R_vir.

Blue galaxies have more uniform CGM distributions than red galaxies.

Lyman α and Si III equivalent widths correlate with galaxy sSFR.

Abstract

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_{\odot} $, and over a range of impact parameters extending to just beyond the halo virial radius ($\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.