Characterizing dw1335-29, a recently discovered dwarf satellite of M83

The number, distribution and properties of dwarf satellites are crucial probes of the physics of galaxy formation at low masses and the response of satellite galaxies to the tidal and gas dynamical effects of their more massive parent. To make progress, it is necessary to augment and solidify the census of dwarf satellites of galaxies outside the Local Group. Muller et al. presented 16 dwarf galaxy candidates near M83, but lacking reliable distances, it is unclear which candidates are M83 satellites. Using red-giant-branch stars from the HST/GHOSTS survey in conjunction with ground-based images from VLT/VIMOS, we confirm that one of the candidates, dw1335-29 - with a projected distance of 26 kpc from M83 and a distance modulus of (m - M)(0) = 28.5(-0.1)(+0.3) - is a satellite of M83. We estimate an absolute magnitude M-V = -10.1 +/- 0.4, an ellipticity of 0.40(-0.22)(+0.14), a half-light radius of 656(-170)(+121) pc and [Fe/H] = -1.3(-0.4)(+0.3). Owing to dw1335-29' s somewhat irregular shape and possible young stars, we classify this galaxy as a dwarf irregular or transition dwarf. This is curious, as with a projected distance of 26 kpc from M83, dw1335-29 is expected to lack recent star formation. Further study of M83' s dwarf population will reveal if star formation in its satellites is commonplace (suggesting a lack of a hot gas envelope for M83 that would quench star formation) or rare (suggesting that dw1335-29 has a larger M83-centric distance, and is fortuitously projected to small radii).