Dark-ages reionization & galaxy formation simulation V: morphology and
  statistical signatures of reionization
  We use the Dark-ages, Reionization And Galaxy-formation Observables from
Numerical Simulations (DRAGONS) framework to investigate the effect of
galaxy-formation physics on the morphology and statistics of ionized hydrogen
(HII) regions during the Epoch of Reioinization (EoR). DRAGONS
self-consistently couples a semi-analytic galaxy-formation model with the
inhomogeneous ionizing UV background, and can therefore be used to study the
dependence of morphology and statistics of reionization on feedback phenomena
of the ionizing source galaxy population. Changes in galaxy-formation physics
modify the sizes of HII regions and the amplitude and shape of 21-cm power
spectra. Of the galaxy physics investigated, we find that supernova feedback
plays the most important role in reionization, with HII regions up to $\approx
20$ per cent smaller and a fractional difference in the amplitude of power
spectra of up to $\approx 17$ per cent at fixed ionized fraction in the absence
of this feedback. We compare our galaxy-formation-based reionization models
with past calculations that assume constant stellar-to-halo mass ratios and
find that with the correct choice of minimum halo mass, such models can mimic
the predicted reionization morphology. Reionization morphology at fixed neutral
fraction is therefore not uniquely determined by the details of galaxy
formation, but is sensitive to the mass of the haloes hosting the bulk of the
ionizing sources. Simple EoR parametrizations are therefore accurate predictors
of reionization statistics. However, a complete understanding of reionization
using future 21-cm observations will require interpretation with realistic
galaxy-formation models, in combination with other observations.
