A close look at the Centaurus A group of galaxies

III. Recent star formation histories of late-type dwarfs around M 83

¹ Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstrasse 12-14, 69120 Heidelberg, Germany
e-mail: denija@ari.uni-heidelberg.de
² School of Mathematics & Physics, University of Tasmania, Private Bag 37 Hobart, 7001 Tasmania, Australia

Received: 27 July 2010
Accepted: 17 February 2011

Abstract

Aims. We study the resolved stellar populations of dwarf galaxies in the nearby Centaurus A/M 83 group of galaxies. Our goal is to characterize their evolutionary history and to investigate eventual similarities or differences with the dwarf population in other group environments.

Methods. This work presents the analysis of five late-type (irregular) dwarfs found in the vicinity of the giant spiral M 83. Using archival HST/ACS data, we perform synthetic color − magnitude diagram modeling to derive the star formation histories of these late-type dwarfs.

Results. The target objects show heterogeneous star formation histories, with average star formation rates of 0.08 to 0.70 × 10^-2   M_⊙   yr^-1. Some of them present prolonged, global bursts of star formation (~300−500 Myr). The studied galaxies are all metal-poor ([Fe/H ]  ~  −1.4). We further investigate the spatial extent of different stellar populations, finding that the young stars show a clumpy distribution, as opposed to the smooth, broad extent of the old ones. The actively star forming regions have sizes of  ~100 pc and lifetimes of  ≳ 100 Myr, thus suggesting a stochastic star formation mode for the target dwarf irregular galaxies. The galaxies formed  ~20% to 70% of their stars more than  ~7 Gyr ago.

Conclusions. The studied dwarfs have average star formation rates slightly higher than their analogues in the Local Group, but comparable to those in the M 81 group. Our preliminary sample indicates that the neutral gas content of the target dwarfs does seem to be affected by the group environment: galaxies within a denser region have a much lower M_HI/ ⟨ SFR ⟩  than the isolated ones, meaning that they will exhaust their gas reservoir more quickly.