Discovery of new dwarf galaxy near the isolated spiral galaxy NGC 6503

Abstract

We report the discovery of a new dwarf galaxy (NGC 6503-d1) during the Subaru extended ultraviolet disk survey. It is a likely companion of the spiral galaxy NGC 6503. The resolved images, in the B, V, R, i, and H alpha bands, show an irregular appearance due to bright stars with underlying, smooth and unresolved stellar emission. It is classified as the transition type (dwarf irregular (dIrr)/dwarf spheroidal (dSph)) between the dIrr and dSph types. Its structural properties are similar to those of the dwarfs in the Local Group, with an absolute magnitude M-V similar to -10.5, half-light radius r(e) similar to 400 pc, and central surface brightness mu(0,V) similar to 25.2. Despite the low stellar surface brightness environment, one H II region was detected, though its H alpha luminosity is low, indicating an absence of any appreciable O-stars at the current epoch. The presence of multiple stellar populations is indicated by the color-magnitude diagram of similar to 300 bright resolved stars and the total colors of the dwarf, with the majority of its total stellar mass similar to 4 x 10(6) M-circle dot in an old stellar population.