Absorption Line Search Through Three Local Group Dwarf Galaxy Halos

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 $\sim 0.5R_{\rm vir}$.