A Compact Population of Red Giants in the Blue Compact Dwarf Galaxy UGCA 290

Abstract

We present HST/WFPC2 single-star photometry for the blue dwarf galaxy UGCA 290, whose morphology is intermediate between classic iE Blue Compact Dwarfs and blue dwarfs which exhibit no red background sheet of older stars. The color-magnitude diagram of this galaxy in V and I, extending over six magnitudes, is remarkably similar to that of the star-forming region in the iE Blue Compact Dwarf VII Zw 403. There is no evidence for gaps in its star-formation history over the last billion years, and the color of its red giant branch indicates a very metal-poor stellar population. From the magnitude of the tip of the red giant branch, we derive a distance of 6.7 Mpc, more than twice the distance estimated from the brightest blue supergiants.