Building up the Galactic Halo: The Sagittarius dSph and the globular cluster M22

Abstract

The Sagittarius dwarf spheroidal (Sgr) and a few paculiar Galactic Globular Clusters (GGC) can be considered as building blocks of theGalactic Halo. We present a series of results based on a wide field photometry of the Sgr system and the GGC M22. In particular for Sgr we present: (1) the detection of the RGB-bump, a feature that together with the shape of the RGB can be used to constrain the allowed range of age and metallicity and (2) the detection of a clear blue horizontal branch which probes the existance of a metal poor population. In the case of M22 we present clear evidence that differential reddening is the primary cause for the observed spread of the evolutionary sequences.