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 deltaT(b) similar to 25 mK to similar to 10(-2) mK during overlap (over a frequency interval Deltanu similar to 25 MHz), while the root mean square fluctuations on small scales drop abruptly from [deltaT(b)(2)](1/2) similar to 10 mK to similar 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.