Quasars Probing Galaxies: I. Signatures of Gas Accretion at Redshift Approximately 0.2

TL;DR

This study investigates the kinematics of circumgalactic gas near galaxies at redshift 0.2, revealing that cold gas co-rotates with galaxies and likely inflows, supporting ongoing star formation.

Contribution

It provides new measurements of galaxy rotation and quasar absorption lines, demonstrating that gas inflows are common at low redshift and contribute to galaxy growth.

Findings

Mg II absorption aligns with galaxy rotation signs.

Gas spirals inward, indicating inflow.

Cold flow disks persist at z ≈ 0.2.

Abstract

We describe the kinematics of circumgalactic gas near the galactic plane, combining new measurements of galaxy rotation curves and spectroscopy of background quasars. The sightlines pass within 19--93 kpc of the target galaxy and generally detect Mg II absorption. The Mg II Doppler shifts have the same sign as the galactic rotation, so the cold gas co-rotates with the galaxy. Because the absorption spans a broader velocity range than disk rotation can explain, we explore simple models for the circumgalactic kinematics. Gas spiraling inwards (near the disk plane) offers a successful description of the observations. An Appendix describes the addition of tangential and radial gas flows and illustrates how the sign of the disk inclination produces testable differences in the projected line-of-sight velocity range. This inflow interpretation implies that cold flow disks remain common down to redshift $z \approx 0.2$ and prolong star formation by supplying gas to the disk.