Resolved stellar populations of dwarf galaxies in the Centaurus A/M83 group

Abstract

Dwarf galaxies, fundamental ingredients of galactic structures in our Universe, are ubiquitous and surprisingly heterogeneous systems. The study of such objects in nearby groups is a powerful way of investigating their formation and evolutionary mechanisms. The Centaurus A/M83 group is denser and in a more advanced evolutionary phase than our own Local Group, thus being an appealing target for the study of dwarf galaxies. Its more than 50 dwarf members, with different morphologies and stellar contents, can still be resolved into individual stars (at an average Galactocentric distance of ~4 Mpc). We use optical (HST/ACS) and near-infrared (VLT/ISAAC) photometric data to derive physical properties and evolutionary histories for sixteen dwarfs in this group. Specifically, the predominantly old populations of our target early-type dwarfs show metallicity contents that resemble what is found for Local Group members. However, they intriguingly contain lower intermediate-age population fractions than those found in morphologically similar dwarfs around the Milky Way, thus being more comparable to the M31 companions. We also apply our analysis techniques to the deeper photometric data available for M31 early-type dwarfs. The star formation histories derived for our star-forming late-type dwarf targets reveal that the star formation is quenched for galaxies currently found in the densest group regions. The time-dependent spatial distribution of their stellar populations points toward a stochastic star formation mode in these objects. Our results show that the evolution of dwarf galaxies depends on their mass but that it is, at the same time, heavily influenced by the surrounding environment. The Centaurus A/M83 group, along with other nearby galaxy groups, deserves further attention in order for us to ultimately gain deeper insights into the processes that regulate the evolution of dwarf galaxies.