Warm Dark Matter and Cosmic Reionization
  In models with dark matter made of particles with keV masses, such as a
sterile neutrino, small-scale density perturbations are suppressed, delaying
the period at which the lowest mass galaxies are formed and therefore shifting
the reionization processes to later epochs. In this study, focusing on Warm
Dark Matter (WDM) with masses close to its present lower bound, i.e. around the
$3$ keV region, we derive constraints from galaxy luminosy functions, the
ionization history and the Gunn-Peterson effect. We show that even if star
formation efficiency in the simulations is adjusted to match the observed UV
galaxy luminosity functions in both CDM and WDM models, the full distribution
of Gunn-Peterson optical depth retains the strong signature of delayed
reionization in the WDM model. However, until the star formation and stellar
feedback model used in modern galaxy formation simulations is constrained
better, any conclusions on the nature of dark matter derived from reionization
observables remain model-dependent.
