The Local Group is dominated by two large galaxies (the Milky Way and
Andromeda), each with its own entourage of (several?) dozen
satellites and surrounded by a similar number of field dwarf
galaxies. In the hierarchical picture of galaxy formation the fate of
these satellites is to be torn apart by their own parents to form
streams of debris which will eventually mix, contributing to the
growth of the larger galaxies' stellar halos. Meanwhile today's field
dwarfs will become the next generation satellites.
Evidence of this process in the form of giant streams of stars around
the Milky Way and Andromeda is abundant. Yet it is not clear that the
properties of these four systems (stellar halos, tidal streams,
satellites and field dwarfs) really make sense in this context:
despite the importance of merging in the past, stellar halos contain
very few stars (only ~1%); streams in stellar halos tend to be more
metal rich than the halos themselves; stars in satellite galaxies
trace different abundance patterns than the stars in the halos; and
the morphology, gas content and mass-metallicity relation for field
dwarfs differs from that for satellites.
In this talk I will try to make sense of these apparent
contradictions to the hierarchical scenario and ask what the Local
Group can tell us about galaxy formation in general.