We report the discovery of a new faint dwarf galaxy , which we dub Scl-MM-Dw1 , at a projected distance of \sim 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 \pm 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 ( \gtrsim 10 Gyr , [ Fe/H ] \sim - 2 ) , and an asymptotic giant branch with an age of \sim 500 Myr .
Scl-MM-Dw1 has a half-light radius of r _ { h } =340 \pm 50 pc and an absolute magnitude of M _ { V } = - 10.3 \pm 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 .