Rotation rates, sizes, and star formation efficiencies of a
  representative population of simulated disc galaxies
  We examine the rotation rates, sizes, and star formation (SF) efficiencies of
a representative population of simulated disc galaxies extracted from the
Galaxies-Intergalactic Medium Interaction Calculation (GIMIC) suite of
cosmological hydrodynamic simulations. These simulations include efficient, but
energetically feasible supernova feedback, but have not been tuned in any way
to produce 'realistic' disc galaxies. Yet, they generate a large number of
discs, without requiring extremely high resolution. Over the wide galaxy
stellar mass range, 9.0 < log10[Mstar (Msun)] < 10.5, the simulations reproduce
the observed Tully-Fisher relation, the rotation curves of disc galaxies in
bins of stellar mass, the mass-size relation of disc galaxies, the optical
rotation to virial circular velocity ratio (Vopt/Vvir), and the SF efficiencies
of disc galaxies as inferred from stacked weak lensing and stacked satellite
kinematics observations. They also reproduce the specific star formation rates
of ~L* galaxies but predict too low levels of star formation for low-mass
galaxies, which is plausibly due to the finite resolution of the simulations.
At higher stellar masses, log10[Mstar (\Msun)] > 10.6, the simulated galaxies
are too concentrated and have too high SF efficiencies. We conjecture that this
shortcoming reflects the neglect of feedback from accreting supermassive black
holes in these simulations. We conclude that it is possible to generate a
representative population of disc galaxies that reproduces many of the observed
trends of local disc galaxies using standard numerical hydrodynamic techniques
and a plausible implementation of the "subgrid" astrophysical processes thought
to be relevant to galaxy formation.
