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Observing the reionization epoch through 21-centimetre radiation

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 δTb ∼ 25 mK to ∼10 −2 mK during overlap (over a frequency interval �ν ∼ 25 MHz), while the root mean square fluctuations on small scales drop abruptly from � δT 2 � 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.