Towards a more realistic population of bright spiral galaxies in
  cosmological simulations
  We present an update to the multiphase SPH galaxy formation code by
Scannapieco et al. We include a more elaborate treatment of the production of
metals, cooling rates based on individual element abundances, and a scheme for
the turbulent diffusion of metals. Our SN feedback model now transfers energy
to the ISM in kinetic and thermal form, and we include a prescription for the
effects of radiation pressure from massive young stars on the ISM. We calibrate
our new code on the well studied Aquarius haloes and then use it to simulate a
sample of 16 galaxies with halo masses between 1x10^11 and 3x10^12 M_sun. In
general, the stellar masses of the sample agree well with the stellar mass to
halo mass relation inferred from abundance matching techniques for redshifts
z=0-4. There is however a tendency to overproduce stars at z>4 and to
underproduce them at z<0.5 in the least massive haloes. Overly high SFRs at z<1
for the most massive haloes are likely connected to the lack of AGN feedback in
our model. The simulated sample also shows reasonable agreement with observed
star formation rates, sizes, gas fractions and gas-phase metallicities at
z=0-3. Remaining discrepancies can be connected to deviations from predictions
for star formation histories from abundance matching. At z=0, the model
galaxies show realistic morphologies, stellar surface density profiles,
circular velocity curves and stellar metallicities, but overly flat metallicity
gradients. 15 out of 16 of our galaxies contain disk components with kinematic
disk fraction ranging between 15 and 65 %. The disk fraction depends on the
time of the last destructive merger or misaligned infall event. Considering the
remaining shortcomings of our simulations we conclude that even higher
kinematic disk fractions may be possible for LambdaCDM haloes with quiet merger
histories, such as the Aquarius haloes.
