HST/COS Spectra of Three QSOs That Probe The Circumgalactic Medium of a Single Spiral Galaxy: Evidence for Gas Recycling and Outflow

TL;DR

This study uses UV spectra of three quasars to analyze the circumgalactic medium of a spiral galaxy, revealing evidence of gas recycling and outflows through absorption features and photoionization modeling.

Contribution

First detailed analysis of CGM around a single spiral galaxy using multiple sight lines, showing gas recycling and outflow evidence.

Findings

Detection of H I Lyα absorption in all three sight lines.

Metal lines detected along major-axis sight lines.

Estimated CGM gas mass of approximately 2 billion solar masses.

Abstract

We have used the Cosmic Origins Spectrograph (COS) to obtain far-UV spectra of three closely-spaced QSO sight lines that probe the circumgalactic medium (CGM) of an edge-on spiral galaxy, ESO 157-49, at impact parameters of 74 and 93 kpc near its major axis and 172 kpc along its minor axis. H I Ly\alpha\ absorption is detected at the galaxy redshift in the spectra of all three QSOs, and metal lines of Si III, Si IV, and C IV are detected along the two major-axis sight lines. Photoionization models of these clouds suggest metallicities close to the galaxy metallicity, cloud sizes of ~1 kpc, and gas masses of ~10^4 solar masses. Given the high covering factor of these clouds, ESO 157-49 could harbor ~2x10^9 solar masses of warm CGM gas. We detect no metals in the sight line that probes the galaxy along its minor axis, but gas at the galaxy metallicity would not have detectable metal absorption with ionization conditions similar to the major-axis clouds. The kinematics of the major-axis clouds favor these being portions of a "galactic fountain" of recycled gas, while two of the three minor-axis clouds are constrained geometrically to be outflowing gas. In addition, one of our QSO sight lines probes a second more distant spiral, ESO 157-50, along its major axis at an impact parameter of 88 kpc. Strong H I Ly\alpha\ and C IV absorption only are detected in the QSO spectrum at the redshift of ESO 157-50.