Absorption Line Search Through Three Local Group Dwarf Galaxy Halos

TL;DR

This study investigates UV absorption lines, specifically C IV, in the halos of three Local Group dwarf galaxies, finding limited detections that inform models of gaseous halo composition and ionization processes.

Contribution

It provides the first observational search for C IV absorption in dwarf galaxy halos at the Local Group scale, linking detection rates to halo models and ionization conditions.

Findings

C IV detected in one of six sightlines toward Sextans A

Halo gas mass aligns with cooling, feedback, and star formation rates

C IV detection is limited to within approximately half the virial radius

Abstract

Dwarf galaxies are missing nearly all of their baryons and metals from the stellar disk, presumed to be in a bound halo or expelled beyond the virial radius. The virial temperature for galaxies with $M_{\rm h} \sim 10^9 - 10^{10}$ $M_{\odot}$ is similar to the collisional ionization equilibrium temperature for the C IV ion. We searched for UV absorption from C IV in six sightlines toward three dwarf galaxies in the anti-M31 direction and at the periphery of the Local Group ($D \approx$ 1.3 Mpc; Sextans A, Sextans B, and NGC 3109). The C IV doublet is detected in only one of six sightlines, toward Sextans A, with $\log N({\rm C IV})$ = $13.06 \pm 0.08$. This is consistent with our gaseous halo models, where the halo gas mass is determined by the cooling rate, feedback, and the star formation rate; the inclusion of photoionization is an essential ingredient. This model can also reproduce the higher detection rate of O VI absorption in other dwarf samples (beyond the Local Group), and with C IV only detectable within $\sim 0.5R_{\rm vir}$.