A close look at the Centaurus A group of galaxies II. Intermediate-age
  populations in early-type dwarfs
  We investigate the resolved stellar content of early-type dwarf galaxies in
the CenA group, in order to estimate the fraction of their intermediate-age
populations. 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. 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 low in the target galaxies
(up to ~15% of the total population). These values could be higher by a factor
of two or three, if we consider the observational limitations and the 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 such
fractions, although our sample is too small to draw firm conclusions. Even when
considering our results as lower limits, the intermediate-age population
fractions for the studied dwarfs are clearly much lower than those found in
similar dwarfs around the Milky Way, but comparable to what is seen for the
low-mass M31 companions. Our results confirm the work by Rejkuba et al. (2006)
about early-type dwarfs in the CenA group.
