The star formation history of Local Group Galaxies (Matteo Monelli, IAC-España)

The life-time star formation history of nearby Local Group galaxies can be studied in detail and reliably through color-magnitude diagrams reaching the oldest main sequence turnoffs. The knowledge of the evolutionary history of nearby galaxies, particularly at old ages, offers an alternative approach to high-redshift cosmological studies aimed at understanding how galaxies form and evolve. In this talk I will review the results of two long-term projects investigating the stellar populations and the star formation history of a sample of Local Group galaxies. First, the Local Cosmology from Isolated Dwarfs (LCID) project, focused on six isolated galaxies of different morphological type: two dIrr (IC1613 and Leo A), two transition dIrr/dSph (LGS3 and Phoenix) and the only two isolated dSph in the Local Group (Cetus and Tucana). Deep HST data allowed us to put reliable constraints on the epoch of star formation in these objects. We found that, with the exception of LeoA, all the galaxies formed a dominant fraction of their stellar mass at epochs older than 10 Gyr ago. I will discuss the possible influence of the reionization on evolution of these galaxies, showing that it had a limited effect, if any. A similar approach has been also been applied to the Large and the Small Magellanic Clouds. We are sampling the stellar populations of both galaxies by imaging and spectroscopy of a large number of wide fields at different galactocentric distances. I will discuss the latest results, in particular concerning the stellar population gradients and the occurrence of a disk/halo transition in the LMC.