Adaptive Mesh Refinement Simulations of Galaxy Formation: Exploring
  Numerical and Physical Parameters
  We carry out adaptive mesh refinement (AMR) cosmological simulations of
Milky-Way mass halos in order to investigate the formation of disk-like
galaxies in a {\Lambda}-dominated Cold Dark Matter model. We evolve a suite of
five halos to z = 0 and find gaseous-disk formation in all; however, in
agreement with previous SPH simulations (that did not include a subgrid
feedback model), the rotation curves of all halos are centrally peaked due to a
massive spheroidal component. Our standard model includes radiative cooling and
star formation, but no feedback. We further investigate this angular momentum
problem by systematically modifying various simulation parameters including:
(i) spatial resolution, ranging from 1700 to 212 pc; (ii) an additional
pressure component to ensure that the Jeans length is always resolved; (iii)
low star formation efficiency, going down to 0.1%; (iv) fixed physical
resolution as opposed to comoving resolution; (v) a supernova feedback model
which injects thermal energy to the local cell; and (vi) a subgrid feedback
model which suppresses cooling in the immediate vicinity of a star formation
event. Of all of these, we find that only the last (cooling suppression) has
any impact on the massive spheroidal component. In particular, a simulation
with cooling suppression and feedback results in a rotation curve that, while
still peaked, is considerably reduced from our standard runs.
