MAGIICAT IV. Kinematics of the Circumgalactic Medium and Evidence for Quiescent Evolution Around Red Galaxies

TL;DR

This study investigates the kinematics and properties of MgII absorption in the circumgalactic medium around red and blue galaxies, revealing ongoing outflows in blue galaxies and quiescent evolution in red galaxies over cosmic time.

Contribution

It provides new insights into how galaxy color and redshift influence CGM kinematics and cloud properties, highlighting the role of star formation quenching in CGM evolution.

Findings

Blue galaxies show consistent velocity dispersions across redshift and distance.

Red galaxies exhibit decreasing velocity dispersions and increasing column densities over time.

Red galaxy CGM becomes more quiescent with lower outflow activity at lower redshifts.

Abstract

The equivalent widths of MgII absorption in the circumgalactic medium (CGM) trace the global star formation rate up to $z<6$, are larger for star-forming galaxies than passively-evolving galaxies, and decrease with increasing distance from the galaxy. We delve further into the physics involved by investigating gas kinematics and cloud column density distributions as a function of galaxy color, redshift, and projected distance from the galaxy (normalized by galaxy virial radius, $D/R_{\rm vir}$). For 39 isolated galaxies at $0.3<z_{\rm gal}<1.0$, we have detected MgII absorption in high-resolution ($\Delta v\simeq 6.6$ km/s) spectra of background quasars within a projected distance of $7<D<190$ kpc. We characterize the absorption velocity spread using pixel-velocity two-point correlation functions. Velocity dispersions and cloud column densities for blue galaxies do not differ with redshift nor with $D/R_{\rm vir}$. This suggests that outflows continually replenish the CGM of blue galaxies with high velocity dispersion, large column density gas out to large distances. Conversely, absorption hosted by red galaxies evolves with redshift where the velocity dispersions (column densities) are smaller (larger) at $z_{\rm gal}<0.656$. After taking into account larger possible velocities in more massive galaxies, we find that there is no difference in the velocity dispersions or column densities for absorption hosted by red galaxies with $D/R_{\rm vir}$. Thus, a lack of outflows in red galaxies causes the CGM to become more quiescent over time, with lower velocity dispersions and larger column densities towards lower $z_{\rm gal}$. The quenching of star formation appears to affect the CGM out to $D/R_{\rm vir}=0.75$.