Stellar Disks in Aquarius Dark Matter Haloes
  We investigate the gravitational interactions between live stellar disks and
their dark matter halos, using LCDM haloes similar in mass to that of the Milky
Way taken from the Aquarius Project. We introduce the stellar disks by first
allowing the haloes to respond to the influence of a growing rigid disk
potential from z = 1.3 to z = 1.0. The rigid potential is then replaced with
star particles which evolve self-consistently with the dark matter particles
until z = 0.0. Regardless of the initial orientation of the disk, the inner
parts of the haloes contract and change from prolate to oblate as the disk
grows to its full size. When the disk normal is initially aligned with the
major axis of the halo at z=1.3, the length of the major axis contracts and
becomes the minor axis by z=1.0. Six out of the eight disks in our main set of
simulations form bars, and five of the six bars experience a buckling
instability that results in a sudden jump in the vertical stellar velocity
dispersion and an accompanying drop in the m=2 Fourier amplitude of the disk
surface density. The bars are not destroyed by the buckling but continue to
grow until the present day. Bars are largely absent when the disk mass is
reduced by a factor of two or more; the relative disk-to-halo mass is therefore
a primary factor in bar formation and evolution. A subset of the disks is
warped at the outskirts and contains prominent non-coplanar material with a
ring-like structure. Many disks reorient by large angles between z=1 and z=0,
following a coherent reorientation of their inner haloes. Larger reorientations
produce more strongly warped disks, suggesting a tight link between the two
phenomena. The origins of bars and warps appear independent: some disks with
strong bars show no disturbances at the outskirts, while the disks with the
weakest bars show severe warps.
