Promising Observational Methods for Detecting the Epoch of Reionization

Abstract

It has been several years since the first detection of Gunn-Peterson troughs in the z > 6 Ly-alpha forest and since the first measurement of the Thomson scattering optical depth through reionization from the cosmic microwave background (CMB). Present day CMB measurements provide a significant constraint on the mean redshift of reionization, and the Ly-alpha forest provides a lower bound on the redshift at which reionization ended. However, no observation has provided definitive information on the duration and morphology of this process. This article is intended as a short review on the most promising observational methods that aim to detect and study this cosmic phase transition, focusing on CMB anisotropies, gamma ray burst afterglows, Ly-alpha emitting galaxies, and redshifted 21cm emission.