* Astronomy

Title: Antlia B: A faint dwarf galaxy member of the NGC 3109 association
Author: D. J. Sand, K. Spekkens, D. Crnojevic, J. R. Hargis, B. Willman, J. Strader, C.J. Grillmair

We report the discovery of Antlia B, a faint dwarf galaxy at a projected distance of ~72 kpc from NGC 3109 (MV~-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±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]~-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 \ion{H}{1} gas at a velocity of vhelio,HI=376 km s^-1, confirming the association with NGC 3109 (vhelio=403 km s^-1). The HI gas mass (MHI=2.8±0.2 x 10⁵ solar masses), stellar luminosity (MV=-9.7±0.6 mag) and half light radius (rh=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 Lambda+Cold Dark Matter model in the sub-Milky Way regime.

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