Observing the reionization epoch through 21-centimetre radiation

Abstract

We study the observability of the reionization epoch through the 21-cm hyperfine transition of neutral hydrogen. We use a high-resolution cosmological simulation (including hydrodynamics) together with a fast radiative transfer algorithm to compute the evolution of 21-cm emission from the intergalactic medium (IGM) in several different models of reionization. We show that the mean brightness temperature of the IGM drops from δT_b∼ 25 mK to ∼10−² mK during overlap (over a frequency interval Δν ∼ 25 MHz), while the root mean square fluctuations on small scales drop abruptly from 〈δT²_b〉¹/² ∼ 10 mK to ∼ 10⁻¹ mK at the end of overlap. We show that 21-cm observations can efficiently discriminate models with a single early reionization epoch from models with two distinct reionization episodes.