DIISC -- VI (COS-DIISC): UV Metal Absorption Relative to the H I disk of Galaxies

TL;DR

This study investigates UV metal absorption features in the circumgalactic medium of nearby galaxies, revealing how metal distribution and properties vary with distance from galaxy centers, and emphasizing the importance of H I radius over virial radius.

Contribution

It presents new observational insights into the spatial distribution of metals around galaxy H I disks using quasar absorption lines, highlighting the significance of H I radius as a better tracer than virial radius.

Findings

Metals are more concentrated closer to galaxies, with higher covering fractions at smaller radii.

Metal absorption features correlate better with H I radius than virial radius.

Cold and cool gas clouds are typically smaller than 2 kpc and often in photoionization equilibrium.

Abstract

As part of the Deciphering the Interplay between the Interstellar medium, Stars, and the Circumgalactic medium (DIISC) survey, we present the UV metal absorption features in the Circumgalactic Medium (CGM) near the H I gas disk ($<$4.5$R_\mathrm{HI}$) of 31 nearby galaxies through quasar absorption line spectroscopy. Of the ions under study, Si III $\lambda1206$ was most frequently detected (18 of 31 sight lines), while C II $\lambda1334$ and Si II $\lambda1260$ were detected in 17 and 15 of 31 sight lines, respectively. Many components were consistent with photoionization equilibrium models, most of the cold and cool gas phase clouds were found to have lengths smaller than 2 kpc. Sight lines with smaller impact parameters ($\rho$) normalized by the galaxy's virial radius ($R_\mathrm{vir}$) and H I radius ($R_\mathrm{HI}$) tend to have more components and larger rest-frame equivalent widths ($W_r$) than those that probe the CGM at larger radii. In particular, we find that the location of metals are better traced by $\rho$ / $R_\mathrm{HI}$ rather than the traditional $\rho$ / $R_\mathrm{vir}$. Larger covering fractions are found closer to galaxies, with a radial decline that depends on the $W_r$ limit used. Our results provide new insights into the spatial distribution of metals around the H I disks of low-redshift galaxies.