Astronomy and Astrophysics – Astrophysics
Scientific paper
2007-09-24
Astron.J.134:1799-1812,2007
Astronomy and Astrophysics
Astrophysics
36 pages, including 11 postscript pages. Astronomical Journal in press
Scientific paper
10.1086/521984
Deep r' and i' images obtained with GMOS on Gemini South are used to probe the bright stellar content in the outer regions of NGC 5253 and ESO269-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 ESO269-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 ESO269-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. Roughly 1 - 10% of the stellar mass of NGC 5253 may have formed during the past few hundred million years, and it is suggested that the progenitors of the two recent SN Ia in this galaxy may have formed at this time. It is argued that the current episodes of star formation in NGC 5253 and ESO269-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 27.48 +/- 0.14 for NGC 5253, and 27.93 +/- 0.18 for ESO269-G058.
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