Idealized models for galactic disk formation and evolution in
  'realistic' LambdaCDM haloes
  We study the dynamics of galactic disk formation and evolution in 'realistic'
LambdaCDM haloes with idealized baryonic initial conditions. We add rotating
spheres of hot gas at z=1.3 to two fully cosmological dark-matter-only halo
(re)simulations. The gas cools according to an artificial and adjustable
cooling function to form a rotationally supported galaxy. The simulations
evolve in the full cosmological context until z=0. We vary the angular momentum
and density profiles of the initial gas sphere, the cooling time and the
orientation of the angular momentum vector to study the effects on the
evolution of the disk. The final disks show realistic structural and kinematic
properties. The slower the cooling/accretion processes, the higher the
kinematic disk-to-bulge ratio D/B of the resulting system. We find that the
initial orientation of the gas angular momentum with respect to the halo has a
major effect on the resulting D/B. The most stable systems result from
orientations parallel to the halo minor axis, but the sign of the spin can have
a strong effect. Despite the spherical and coherently rotating initial gas
distribution, the orientation of the central disk and of the outer gas
components and the relative angle between the components can all change by more
than 90 degrees over several billion years. Disks can form from initial
conditions oriented parallel to the major axis, but there is often strong
misalignment between inner and outer material. The more the orientation of the
baryonic angular momentum changes during the evolution, the lower the final
D/B. The behaviour varies strongly from halo to halo. Even our simple initial
conditions can lead to strong bars, dominant bulges, massive, misaligned rings
and counter-rotating components. We discuss how our results may relate to the
failure or success of fully cosmological disk formation simulations. (abridged)
