NGC 5253 and ESO 269-G058: Dwarf Galaxies with a Past

Abstract

Deep r' and i' images obtained with GMOS on Gemini South are used to probe the bright stellar content in the outer regions of the Centaurus Group dwarf galaxies NGC 5253 and ESO 269-G058. Red giant branch (RGB) stars are traced out to a distance of 8 kpc along the major axis of NGC 5253 and 6 kpc in ESO 269-G058. The outer regions of both galaxies are metal-poor; RGB stars located between projected major axis distances of 2 and 4 kpc in NGC 5253 have [Fe/H] ∼ -1, whereas RGB stars in the corresponding portion of ESO 269-G058 have [Fe/H] ∼ -1.8. Stars with metallicities that differ from the mean by more than a few tenths of a dex make only a modest contribution to the stellar content in the outer regions of both galaxies. A population of bright asymptotic giant branch (AGB) stars is seen in both galaxies. In the particular case of NGC 5253, roughly 1%-10% of the stellar mass may have formed during the past few hundred million years, and it is suggested that the progenitors of the two recent Type Ia supernovae in this galaxy may have formed at this time. That NGC 5253 has experienced either episodic or continuing elevated levels of star formation during the past few hundred million years is reminiscent of what is seen in other dwarf starburst galaxies, such as NGC 3077, and it is argued that the current episodes of star formation in NGC 5253 and ESO 269-G058 may have been triggered up to ∼1 Gyr in the past. Finally, a distance modulus is computed for each galaxy based on the brightness of the RGB tip, and the results are μ0 = 27.48 ± 0.14 for NGC 5253 and 27.93 ± 0.18 for ESO 269-G058.