A Predicted New Population of UV-faint Galaxies at z>4
  We show that a bursty model of high redshift star formation explains several
puzzling observations of the high redshift galaxy population. We begin by
pointing out that the observed specific star formation rate requires a
duty-cycle of ~10%, which is much lower than found in many hydro-dynamical
simulations. This value follows directly from the fact that the observed star
formation rate in galaxies integrated over a Hubble time exceeds the observed
stellar mass by an order of magnitude. We use the large observed specific star
formation rate to calibrate the efficiency of feedback in a model for the high
redshift star formation rate which includes merger driven star formation
regulated by SNe feedback. This model reproduces the star formation rate
density function and the stellar mass function of galaxies at 4<z<7. A
prediction of the model is that the specific star formation rate does not
evolve very rapidly with either mass or redshift, in agreement with
observation. This is in contrast to results from hydrodynamical simulations
where the star formation closely follows the accretion rate, and so increases
strongly towards high redshift. The bursty star formation model naturally
explains the observation that there is not enough stellar mass at z~2-4 to
account for all of the star-formation observed, without invoking properties
like an evolving initial mass function of stars. The finding of a duty cycle
that is ~10% implies that there should be ten times the number of known
galaxies at fixed stellar mass that have not yet been detected through standard
UV selection at high redshift. We therefore predict the existence of a large
undetected population of UV-faint galaxies that accounts for most of the
stellar mass density at z~4-8.
