Dark matter response to galaxy formation
  We have resimulated the six galaxy-sized haloes of the Aquarius Project
including metal-dependent cooling, star formation and supernova feedback. This
allows us to study not only how dark matter haloes respond to galaxy formation,
but also how this response is affected by details of halo assembly history. In
agreement with previous work, we find baryon condensation to lead to increased
dark matter concentration. Dark matter density profiles differ substantially in
shape from halo to halo when baryons are included, but in all cases the
velocity dispersion decreases monotonically with radius. Some haloes show an
approximately constant dark matter velocity anisotropy with $ \beta \approx
0.1-02$, while others retain the anisotropy structure of their baryon-free
versions. Most of our haloes become approximately oblate in their inner
regions, although a few retain the shape of their dissipationless counterparts.
Pseudo-phase-space densities are described by a power law in radius of altered
slope when baryons are included. The shape and concentration of the dark matter
density profiles are not well reproduced by published adiabatic contraction
models. The significant spread we find in the density and kinematic structure
of our haloes appears related to differences in their formation histories. Such
differences already affect the final structure in baryon-free simulations, but
they are reinforced by the inclusion of baryons, and new features are produced.
The details of galaxy formation need to be better understood before the inner
dark matter structure of galaxies can be used to constrain cosmological models
or the nature of dark matter.
