We report the discovery of a new faint dwarf galaxy, which we dub Scl-MM-Dw1, at a projected distance of ∼65 kpc from the spiral galaxy NGC 253. The discovery results from the Panoramic Imaging Survey of Centaurus and Sculptor (PISCeS), a program with the Magellan/Megacam imager to study faint substructure in resolved stellar light around massive galaxies outside of the Local Group. We measure a tip of the red giant branch distance to Scl-MM-Dw1 of D=3.9±0.5 Mpc, consistent with that of NGC 253, making their association likely. The new dwarf's stellar population is complex, with an old, metal poor red giant branch (≳10 Gyr, [Fe/H]∼−2), and an asymptotic giant branch with an age of ∼500 Myr. Scl-MM-Dw1 has a half-light radius of rh=340±50 pc and an absolute magnitude of MV=−10.3±0.6 mag, comparable to the Milky Way's satellites at the same luminosity. Once complete, our imaging survey of NGC 253 and other nearby massive galaxies will provide a census of faint substructure in halos beyond the Local Group, both to put our own environment into context and to confront models of hierarchical structure formation.
@article{arxiv.1406.6687,
title = {Discovery of a new faint dwarf galaxy associated with NGC 253},
author = {D. J. Sand and D. Crnojević and J. Strader and E. Toloba and J. D. Simon and N. Caldwell and P. Guhathakurta and B. McLeod and A. C. Seth},
journal= {arXiv preprint arXiv:1406.6687},
year = {2015}
}