A close look at the Centaurus A group of galaxies: IV. Recent star formation histories of late-type dwarfs around CenA

<p><b>Aims:</b> We study a sample of five dwarf irregular galaxies in the CenA/M 83 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.</p> <p><b>Methods:</b> 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.</p><p> </p><p><b>Results:</b> The average star formation rate for the studied galaxies ranges from 10^-3 M⊙ yr^-1 up to ~ 7 x 10^-2 M⊙ yr^-1, and their mean metallicities correlate with their luminosities (from [Fe/H] ~ -1.4 up to ~ -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.</p> <b>Conclusions:</b> The resulting star formation histories for the CenA companions are similar to those found for comparable Local Group and M 81 group dwarfs. We consider this sample of dwarfs together with five previously studied M 83 dwarf irregular companions. We find no trend of the <i>average</i> star formation rate with tidal index or distance from the main galaxy of the group. However, dwarfs with higher baryonic masses do show higher <i>average</i> 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 <i>recent</i> (~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.