The star formation history of dwarf spheroidal galaxies

By means of N-body/hydro-dynamical simulations that include star formation, feedback and chemical evolution we attempt to model the formation and evolution of dwarf spheroidals galaxies, like those ones of the Local Group. We start from virialized haloes of dark matter, and follow the infall of gas into the potential wells and the formation of stars. We find that in objects of the same total mass, different star formation histories are possible, if the collapse phase started at different initial densities (redshifts). We predict the final structure of dwarf spheroidal galaxies, their kinematics, their large scale distribution of gas and stars, and their detailed histories of the star formation and metal enrichment. Basing on the population synthesis technique, star formation (SF) and metal enrichment rates are then used to generate the present color-magnitude diagrams (CMDs) of the stellar populations hosted by dwarf spheroidal galaxies as a function of different cosmological models that fix the relationship between redshift of formation, age of the universe, and galactic ages. The resulting CMDs are then compared with the observational ones for some dwarf spheroidals of the Local Group.