The Growth of HiiRegions During Reionization

Recently, there has been a great deal of interest in understanding thereionization of hydrogen in the intergalactic medium (IGM). One of the majoroutstanding questions is how this event proceeds on large scales. Motivated bynumerical simulations, we develop a model for the growth of HII regions duringthe reionization era. We associate ionized regions with large-scale densityfluctuations and use the excursion set formalism to model the resulting sizedistribution. We then consider ways in which to characterize the morphology ofionized regions. We show how to construct the power spectrum of fluctuations inthe neutral hydrogen field. The power spectrum contains definite features fromthe HII regions that should be observable with the next generation oflow-frequency radio telescopes through surveys of redshifted 21 cm emissionfrom the reionization era. Finally, we also consider statistical descriptionsbeyond the power spectrum and show that our model of reionization qualitativelychanges the distribution of neutral gas in the IGM.Comment: 14 pages, 13 figures, submitted to Ap