Radiative feedback and the low efficiency of galaxy formation in
  low-mass haloes at high redshift
  Any successful model of galaxy formation needs to explain the low rate of
star formation in the small progenitors of today's galaxies. This inefficiency
is necessary for reproducing the low stellar-to-virial mass fractions,
suggested by current abundance matching models. A possible driver of this low
efficiency is the radiation pressure exerted by ionizing photons from massive
stars. The effect of radiation pressure in cosmological, zoom-in galaxy
formation simulations is modeled as a non-thermal pressure that acts only in
dense and optically thick star-forming regions. We also include photoionization
and photoheating by massive stars. The full photoionization of hydrogen reduces
the radiative cooling in the $10^{4-4.5}$ K regime. The main effect of
radiation pressure is to regulate and limit the high values of gas density and
the amount of gas available for star formation. This maintains a low star
formation rate of $\sim 1 \ {\rm M_\odot} \ {\rm yr}^{-1}$ in halos with masses
about $10^{11} \ {M_\odot}$ at $z\simeq3$. Infrared trapping and
photoionization/photoheating processes are secondary effects in this mass
range. The galaxies residing in these low-mass halos contain only $\sim0.6\%$
of the total virial mass in stars, roughly consistent with abundance matching.
Radiative feedback maintains an extended galaxy with a rising circular velocity
profile.
