We report the discovery of Antlia B , a faint dwarf galaxy at a projected distance of \sim 72 kpc from NGC 3109 ( M _ { V } \sim - 15 mag ) , the primary galaxy of the NGC 3109 dwarf association at the edge of the Local Group .
The tip of the red giant branch distance to Antlia B is D =1.29 \pm 0.10 Mpc , which is consistent with the distance to NGC 3109 .
A qualitative analysis indicates the new dwarf ’ s stellar population has both an old , metal poor red giant branch ( \gtrsim 10 Gyr , [ Fe/H ] \sim - 2 ) , and a younger blue population with an age of \sim 200-400 Myr , analogous to the original Antlia dwarf , another likely satellite of NGC 3109 .
Antlia B has H i gas at a velocity of v _ { helio,HI } =376 km s ^ { -1 } , confirming the association with NGC 3109 ( v _ { helio } =403 km s ^ { -1 } ) .
The H i gas mass ( M _ { HI } =2.8 \pm 0.2 \times 10 ^ { 5 } M _ { \odot } ) , stellar luminosity ( M _ { V } = - 9.7 \pm 0.6 mag ) and half light radius ( r _ { h } =273 \pm 29 pc ) are all consistent with the properties of dwarf irregular and dwarf spheroidal galaxies in the Local Volume , and is most similar to the Leo P dwarf galaxy .
The discovery of Antlia B is the initial result from a Dark Energy Camera survey for halo substructure and faint dwarf companions to NGC 3109 with the goal of comparing observed substructure with expectations from the \Lambda +Cold Dark Matter model in the sub-Milky Way regime .