Kinematics of the Circumgalactic Medium of a $z = 0.77$ Galaxy from MgII Tomography

• Main Authors: Mortensen, Kris, C, Keerthi Vasan G, Jones, Tucker, Faucher-Giguere, Claude-Andre, Sanders, Ryan, Ellis, Richard S, Leethochawalit, Nicha, Stark, Daniel P
• Format: Journal Article
• Language: English
• Published: 29-05-2020
• Subjects: Physics - Astrophysics of Galaxies
• DOI: 10.48550/arxiv.2006.00006

Galaxy evolution is thought to be driven in large part by the flow of gas
between galaxies and the circumgalactic medium (CGM), a halo of metal-enriched
gas extending out to $\gtrsim100$ kpc from each galaxy. Studying the spatial
structure of the CGM holds promise for understanding these gas flow mechanisms;
however, the common method using background quasar sightlines provides minimal
spatial information. Recent works have shown the utility of extended background
sources such as giant gravitationally lensed arcs. Using background lensed arcs
from the CSWA 38 lens system, we continuously probed, at a resolution element
of about 15 kpc$^2$, the spatial and kinematic distribution of MgII absorption
in a star-forming galaxy at $z=0.77$ (stellar mass $\approx 10^{9.7}$
M$_\odot$, star formation rate $\approx 10$ M$_\odot$ yr$^{-1}$) at impact
parameters $D \simeq 5-30$ kpc. Our results present an anisotropic, optically
thick medium whose absorption strength decreases with increasing impact
parameter, in agreement with the statistics towards quasars and other
gravitational arcs. Furthermore, we find generally low line-of-sight velocities
in comparison to the relatively high velocity dispersion in the MgII gas (with
typical $\sigma\approx 50$ km s$^{-1}$). While the galaxy itself exhibits a
clear outflow (with MgII velocities up to $\sim 500$ km s$^{-1}$) in the
down-the-barrel spectrum, the outflow component is sub-dominant and only weakly
detected at larger impact parameters probed by the background arcs. Our results
provide evidence of mainly dispersion-supported, metal-enriched gas recycling
through the CGM.