The Dynamical Evolution of Substructure
B. Zhang, R.F.G. Wyse, M. Stiavelli, J. Silk, MNRAS, in press
The evolution of clumpy structure 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. The ratio of the
internal clump velocity dispersion to that of the dark halo is an
as this ratio approaches a value
of unity, heating by close encounters between clumps becomes less
important while the other dynamical processes continue to increase in
importance. Our comparison between merging and disruption processes
implies that spiral galaxies cannot be formed in a proto-system that
contains a few large clumps, with merging as the dominant process, 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 clumpy
structure is not sufficient to form a cD galaxy, with an extended
envelope, but subsequent accretion of large galaxies is required.
The post-collapse system is in general triaxial, with rounder systems
resulting from fewer, but more massive, clumps.
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 29\%
of the sky.
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