A dwarf irregular galaxy at the edge of the Local Group: Stellar populations and distance of IC 5152

Abstract

We have obtained V and I-band photometry for about 700 stars in the field of the dwarf irregular galaxy IC 5152, previously considered a possible member of the Local Group. Deep VI color-magnitude diagrams are presented of the main body of this galaxy and of a nearby field. We infer a distance by comparison with the VI color-magnitude diagrams of similar galaxies and with theoretical isochrones. The distance modulus to IC 5152 is found to be m-Mo = 26.15 +/- 0.2, adopting E(V-I) = 0. This distance of D=1.7 Mpc implies that IC 5152 is not a certain member of the Local Group. We also construct a deep optical luminosity function. By comparison with theoretical isochrones, we find a metallicity Z of approximately 0.002, which is lower than previous estimates. Using this metallicity and distance, IC 5152 now fits the metallicity-luminosity relation for dwarf galaxies. The youngest stars in the field studied have an age of ~10^7 Gyr, and there is a substantial population of stars with log t>7.8-8 yr. The central region of IC 5152 is an active site of star formation, as found by comparing our optical photometry with Hubble Space Telescope ultraviolet images. Several candidate globular clusters are found, as well as a candidate for a potential nucleus.