NIHAO project I: Reproducing the inefficiency of galaxy formation across
  cosmic time with a large sample of cosmological hydrodynamical simulations
  We introduce project NIHAO (Numerical Investigation of a Hundred
Astrophysical Objects), a set of 100 cosmological zoom-in hydrodynamical
simulations performed using the gasoline code, with an improved implementation
of the SPH algorithm. The haloes in our study range from dwarf to Milky Way
masses, and represent an unbiased sampling of merger histories, concentrations
and spin parameters. The particle masses and force softenings are chosen to
resolve the mass profile to below 1% of the virial radius at all masses,
ensuring that galaxy half-light radii are well resolved. Using the same
treatment of star formation and stellar feedback for every object, the
simulated galaxies reproduce the observed inefficiency of galaxy formation
across cosmic time as expressed through the stellar mass vs halo mass relation,
and the star formation rate vs stellar mass relation. We thus conclude that
stellar feedback is the chief piece of physics required to limit the efficiency
of star formation in galaxies less massive than the Milky Way.
