A close look at the Centaurus A group of galaxies. II. Intermediate-age populations in early-type dwarfs
Rejkuba, M.; Crnojević, D.; Grebel, E. K.; Da Costa, G.; Jerjen, H.
Germany, Australia
Abstract
Aims: We investigate the resolved stellar content of early-type dwarf galaxies in the Centaurus A group, to estimate their intermediate-age population fractions.
Methods: We use near-infrared photometric data taken with the VLT/ISAAC instrument, together with previously analyzed archival HST/ACS data. The combination of the optical and infrared wavelength range permits us to firmly identify luminous asymptotic giant branch stars, which are indicative of an intermediate-age population in these galaxies.
Results: We consider one dwarf spheroidal (CenA-dE1) and two dwarf elliptical (SGC1319.1-4216 and ESO269-066) galaxies that are dominated by an old population. The most recent periods of star formation are estimated to have taken place between ~2 and ~5 Gyr ago for SGC1319.1-4216 and ESO269-066, and approximately 9 Gyr ago for CenA-dE1. For ESO269-066, we find that the intermediate-age populations are significantly more centrally concentrated than the predominantly old underlying stars. The intermediate-age population fraction is found to be small in the target galaxies, consistent with fractions of up to ~15% of the total population. These values might be larger by a factor of two or three, if we considered the observational limitations and recent discussion about the uncertainties in theoretical models. We suggest that there is a correlation between intermediate-age population fraction and proximity to the dominant group galaxy, with closer dwarfs having slightly smaller fractions, although our sample is too small to draw firm conclusions.
Conclusions: Even when considering our results as lower limits, the intermediate-age population fractions for the studied dwarfs are clearly much smaller than those found in similar dwarfs around the Milky Way, but comparable to what is seen for the low-mass M 31 companions. Our results confirm our previous work about early-type dwarfs in the Centaurus A group.