The effects of radiative transfer on the reionization of an inhomogeneous universe

Assuming simple dynamics for the growth of density fluctuations, we impleme nt six-dimensional (6D) radiative transfer calculations to elucidate the ef fects of photon propagation during the reionization of an inhomogeneous uni verse. The ionizing sources are postulated to be AGN-like in this paper. Th e present simulations reveal that radiative transfer effects are still prom inent considerably after the percolation epoch, in which patchy ionized reg ions connect with each other. In other words, owing to the collective opaci ty, the Universe does not become perfectly transparent against ionizing rad iation even though strongly self-shielded regions disappear. It turns out t hat the inhomogeneity of the medium enhances the opacity effects and delays the end of reionization. Owing to such radiative transfer effects, the rei onization in an inhomogeneous universe proceeds fairly slowly, in contrast to the prompt reionization in a homogeneous universe, and as a result the s urface of reionization is not so sharply edged, but highly uneven. As a sig nature of the uneven surface of reionization, the cosmic IR background (CIB ) radiation, which is produced by Ly alpha photons resulting from radiative recombination, could exhibit strong anisotropies, reflecting the amplitude of density fluctuations at the reionization era. The predicted CIB intensi ty lies on a level of possible detection by forthcoming IR space telescope facilities.