  The evolution of substructure embedded in non-dissipative dark halos is
studied through N-body simulations of isolated systems, both in and out of
initial equilibrium, complementing cosmological simulations of the growth of
structure. We determine by both analytic calculations and direct analysis of
the N-body simulations the relative importance of various dynamical processes
acting on the clumps, such as the removal of material by global tides,
clump-clump heating, clump-clump merging and dynamical friction. Our comparison
between merging and disruption processes implies that spiral galaxies cannot be
formed in a proto-system that contains a few large clumps, but can be formed
through the accretion of many small clumps; elliptical galaxies form in a more
clumpy environment than do spiral galaxies. Our results support the idea that
the central cusp in the density profiles of dark halos is the consequence of
self-limiting merging of small, dense halos. This implies that the collapse of
a system of clumps/substructure is not sufficient to form a cD galaxy, with an
extended envelope; plausibly subsequent accretion of large galaxies is
required. Persistent streams of material from disrupted clumps can be found in
the outer regions of the final system, and at an overdensity of around 0.75,
can cover 10% to 30% of the sky.
