Dwarf Galaxies: the building blocks of the Milky Way?

In hierarchical clustering scenarios of galaxy formation, such as cold dark matter-dominated cosmologies (White and Rees 1978), dwarf galaxies should have formed prior to the epoch of giant galaxy formation and would be the building blocks of larger galaxies. The picture of building the Galactic halo from merging ``fragments'', which Searle and Zinn (1978) proposed on the basis of the properties of the Milky Way globular clusters, is regarded as the local manifestation of this galaxy formation scenario. The Milky Way continues to be one of the best places to test this picture. This is supported by, for example, the discovery of the Sagittarius dwarf galaxy (Ibata, Gilmore and Irwin 1994) in the process of merging with the Galactic halo, the identification of isolated stellar tidal streams in the halo and the possibility that several dwarf spheroidals (dSph) and outer globular clusters lie along two distinct streams that may be the remnants of larger parent satellite galaxies or Searle and Zinn ``fragments''. The possibility that merger events may leave an observable fossil record in the halo is also supported by theoretical models of tidally disrupted dSph satellites . In this talk I present the first results of a long-term project to investigate the process of accretion and tidal disruption of dSph satellites in the Galactic halo, to ultimately constrain which fraction has its origin in such events. These includes new insights on the Sagittarius tidal stream, the tidal disruption of Ursa Minor and Draco dSph, the dark matter content in Local Group dSph and the existence of remnants of tidally disrupted dSph around a sample of remote young globular clusters.