Bursty star formation during the Cosmic Dawn driven by delayed stellar
  feedback
  In recent years, several analytic models have demonstrated that simple
assumptions about halo growth and feedback-regulated star formation can match
the (limited) existing observational data on galaxies at z>6. By extending such
models, we demonstrate that imposing a time delay on stellar feedback (as
inevitably occurs in the case of supernova explosions) induces burstiness in
small galaxies. Although supernova progenitors have short lifetimes (~5-30
Myr), the delay exceeds the dynamical time of galaxies at such high redshifts.
As a result, star formation proceeds unimpeded by feedback for several cycles
and "overshoots" the expectations of feedback-regulated star formation models.
We show that such overshoot is expected even in atomic cooling halos, with
masses up to ~10^10.5 Msun at z>6. However, these burst cycles damp out quickly
in massive galaxies, because large haloes are more resistant to feedback so
retain a continuous gas supply. Bursts in small galaxies - largely beyond the
reach of existing observations - induce a scatter in the luminosity of these
haloes (of ~1 mag) and increase the time-averaged star formation efficiency by
up to an order of magnitude. This kind of burstiness can have substantial
effects on the earliest phases of star formation and reionization.
