  We study a sample of 5 dwarf irregular galaxies in the CenA/M83 group, which
are companions to the giant elliptical CenA. We aim at deriving their physical
properties over their lifetime and compare them to those of dwarfs located in
different environments. We use archival HST/ACS data and apply synthetic
color-magnitude diagram fitting in order to reconstruct the past star formation
activity of the target galaxies. The average star formation rate for the
studied galaxies ranges from 10^{-3} up to \sim 7x10^{-2} M_odot/yr, and their
mean metallicities correlate with their luminosities (from [Fe/H]\sim -1.4 up
to \sim -1.0). The form of the star formation histories varies across the
sample, with quiescent periods alternating with intermittent enhancements in
the star formation (from a few up to several times the average lifetime value).
The dwarfs in this sample formed ~35% to ~60% of their stellar content prior to
~5 Gyr ago. The resulting star formation histories for the CenA companions are
similar to those found for comparable Local Group and M81 group dwarfs. We
consider this sample of dwarfs together with 5 previously studied M83 dwarf
irregular companions. We find no trend of the average star formation rate with
tidal index or distance from the main galaxy of the group. However, dwarfs with
higher baryonic masses do show higher average star formation rates, underlining
the importance of intrinsic properties in governing the evolution of these
galaxies. On the other hand, there is also a clear trend when looking at the
recent (~0.5-1 Gyr) level of activity. Namely, dwarfs within a denser region of
the group appear to have had their star formation quenched while dwarfs located
in the group outskirts show a wide range of possible star formation rates, thus
indicating that external processes play a fundamental role, complementary to
mass, in shaping the star formation histories of dwarf galaxies.

Cosmology and Nongalactic Astrophysics