Statistical Probes of Reionization with 21 Centimeter Tomography

We consider the degree to which "21 cm tomography" of the high-redshiftUniverse can distinguish different ionization histories. Using a new analyticmodel for the size distribution of HII regions that associates these ionizedbubbles with large-scale galaxy overdensities, we compute the angular powerspectrum and other statistical properties of the 21 cm brightness temperatureduring reionization. We show that the HII regions imprint features on the powerspectrum that allow us to separate histories with discrete bubbles from thosewith partial uniform ionization (by, for example, X-rays). We also show that"double reionization" scenarios will modify the morphology of the bubbles inways that depend on the mechanism through which the first generation of sourcesshuts off. If, for example, the transition occurs globally at a fixed redshift,the first generation imprints a persistent feature on the 21 cm power spectrum.Finally, we compare our model to one in which voids are ionized first. Whilethe power spectra of these two models are qualitatively similar, we show thatthe underlying distributions of neutral hydrogen differ dramatically andsuggest that other statistical tests can distinguish them. The next generationof low-frequency radio telescopes will have the sensitivity to distinguish allof these models and strongly constrain the history and morphology ofreionization.Comment: 6 pages, 4 figures, submitted to Ap