The formation of disc galaxies in a LCDM universe
  We study the formation of disc galaxies in a fully cosmological framework
using adaptive mesh refinement simulations. We perform an extensive parameter
study of the main subgrid processes that control how gas is converted into
stars and the coupled effect of supernovae feedback. We argue that previous
attempts to form disc galaxies have been unsuccessful because of the universal
adoption of strong feedback combined with high star formation efficiencies.
Unless extreme amounts of energy are injected into the interstellar medium
during supernovae events, these star formation parameters result in bulge
dominated S0/Sa galaxies as star formation is too efficient at z~3. We show
that a low efficiency of star-formation more closely models the subparsec
physical processes, especially at high redshift. We highlight the successful
formation of extended disc galaxies with scale lengths r_d=4-5 kpc, flat
rotation curves and bulge to disc ratios of B/D~1/4. Not only do we resolve the
formation of a Milky Way-like spiral galaxy, we also observe the secular
evolution of the disc as it forms a pseudo-bulge. The disc properties agree
well with observations and are compatible with the photometric and baryonic
Tully-Fisher relations, the Kennicutt-Schmidt relation and the observed angular
momentum content of spiral galaxies. We conclude that underlying small-scale
star formation physics plays a larger role than previously considered in
simulations of galaxy formation.
