2015ApJ...812L..13S

We report the discovery of Antlia B, a faint dwarf galaxy at a projected distance of ∼72 kpc from NGC 3109 (), 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±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 ( [Fe/H] ∼ -2), and a younger blue population with an age of ∼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 = 376 km/s, confirming the association with NGC 3109 (v_helio= 403 km/s). The H i gas mass (M_ H i_= 2.8±0.2x10⁵), stellar luminosity (M_V= -9.7±0.6 mag) and half light radius (r_h= 273±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 Λ+Cold Dark Matter model in the sub-Milky Way regime.