Spatial segregation impact on star formation in nearby dwarf spheroidal galaxies

Abstract

Using our HST/ACS observations of the recently found isolated dwarf spheroidal galaxies, we homogeneously measured their star formation histories. We determined star formation rate as a function of time, as well as age and metallicity of the stellar populations. All objects demonstrate complex star formation history, with a significant portion of stars formed 10-13 Gyr ago. Nevertheless, stars of middle ages (1-8 Gyr) are presented. In order to understand how the star formation parameters influence the evolution of dSphs, we also studied a sample of nearest dSphs in different environment: isolated (d < 2 Mpc); beyond the Local Group virial radius (but within the Local Group zero velocity sphere); and the satellites of M 31 located within the virial zone (300 kpc). Using archival HST/ACS observations, we measured their star formation histories. A comparative analysis of the parameters obtained allow us to distinguish a possible effect of the spatial segregation on the dSphs evolution scenario.