The impact of stellar feedback on the structure, size and morphology of
  galaxies in Milky Way size dark matter haloes
  We use cosmological zoom-in simulations of galaxy formation in a Milky Way
(MW)-sized halo started from identical initial conditions to investigate the
evolution of galaxy sizes, baryon fractions, morphologies and angular momenta
in runs with different parameters of the star formation--feedback cycle. Our
fiducial model with a high local star formation efficiency, which results in
efficient feedback, produces a realistic late-type galaxy that matches the
evolution of basic properties of late-type galaxies: stellar mass, disk size,
morphology dominated by a kinematically cold disk, stellar and gas surface
density profiles, and specific angular momentum. We argue that feedback's role
in this success is twofold: (1) removal of low-angular momentum gas and (2)
maintaining a low disk-to-halo mass fraction which suppresses disk
instabilities that lead to angular momentum redistribution and a central
concentration of baryons. However, our model with a low local star formation
efficiency, but large energy input per supernova, chosen to produce a galaxy
with a similar star formation history as our fiducial model, leads to a highly
irregular galaxy with no kinematically cold component, overly extended stellar
distribution and low angular momentum. This indicates that only when feedback
is allowed to become vigorous via locally efficient star formation in dense
cold gas, resulting galaxy sizes, gas/stellar surface density profiles and
stellar disk angular momenta agree with observed $z=0$ galaxies.
