Discovery of a new faint dwarf galaxy associated with NGC 253

TL;DR

This paper reports the discovery of a new faint dwarf galaxy near NGC 253, providing insights into faint substructures around massive galaxies beyond the Local Group and contributing to understanding hierarchical galaxy formation.

Contribution

The paper presents the first identification and characterization of a faint dwarf galaxy associated with NGC 253 using the PISCeS survey, expanding knowledge of galaxy satellites beyond the Local Group.

Findings

Discovered a dwarf galaxy at ~65 kpc from NGC 253.

Measured a distance of 3.9 Mpc, consistent with NGC 253.

Determined the galaxy's stellar population and structural properties.

Abstract

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.