Document Type

Journal Article



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Journal Title

Astrophysical Journal Letters





Publication Date



We report the discovery of Antlia B, a faint dwarf galaxy at a projected distance of similar to 72 kpc from NGC 3109 (M-V similar to -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 (greater than or similar to 10 Gyr, [Fe/H] similar to -2), and a younger blue population with an age of similar to 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, H I) = 376 kms(-1), confirming the association with NGC 3109 (v(helio) = 403 km s(-1)). The H I gas mass (M-H I = 2.8 +/- 0.2 x 10(5) M-circle dot), stellar luminosity (M-V = -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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