Antlia B: A faint dwarf galaxy member of the NGC 3109 association

D. J. Sand; K. Spekkens; D. Crnojević; J. R. Hargis; B. Willman; J. Strader; C. J. Grillmair

doi:10.1088/2041-8205/812/1/L13

paper

Antlia B: A faint dwarf galaxy member of the NGC 3109 association

arXiv:1508.01800 · doi:10.1088/2041-8205/812/1/L13

Abstract

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 ( $≳$ 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 \ion{H}{1} gas at a velocity of $v_{h e l i o, H I}$ =376 km s $^{- 1}$ , confirming the association with NGC 3109 ( $v_{h e l i o}$ =403 km s $^{- 1}$ ). The HI gas mass (M $_{H I}$ =2.8 $\pm$ 0.2 $\times$ 10 $^{5}$ M $_{⊙}$ ), 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 $Λ$ +Cold Dark Matter model in the sub-Milky Way regime.

7 pages, 3 figures. Submitted to ApJL

Antlia B: A faint dwarf galaxy member of the NGC 3109 association

Abstract

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