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, which are presumed to be in a bound halo or expelled beyond the virial radius. The virial temperature for galaxies with M _h ~ 10⁹-10¹⁰ M _⊙ is similar to the collisional ionization equilibrium temperature for the C IV ion. We search 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 ≈ 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 $\mathrm{log}N({\rm{C}}\,{\rm\small{IV}})=13.06\pm 0.08$ . 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), with C IV only detectable within ~0.5R _vir.