Spectral features from the reionization epoch

Emission lines in hydrogen can be used to measure the approximate redshift of the reionization of the universe. This is an important measurement given the lack of a convincing theoretical prediction of this epoch. There is a rapid change in absorption at the reionization event, which can leave sharp features in the spectrum of recombining hydrogen. These features in the near-infrared background permit us to measure the redshift at which reionization occurs. We have calculated these signals based on numerical simulations of the ACDM cosmogony.