The Influence of Nonuniform Reionization on the CMB

Abstract

We investigate the impact of spatial variations in the ionized fraction during reionization on temperature anisotropies in the CMB. We combine simulations of large- scale structure to describe the underlying density field with an analytic model based on extended Press- Schechter theory to track the reionization process. We find that the power spectrum of the induced CMB anisotropies depends sensitively on the character of the reionization epoch. Models that differ in the extent of the `` patchy phase'' could be distinguished by future experiments such as the Atacama Cosmology Telescope ( ACT) and the South Pole Telescope ( SPT). In our models, the patchy signal peaks at l similar or equal to 2000, where it can be 4 times larger than the kinetic Sunyaev- Zel'dovich ( kSZ)/ Ostriker- Vishniac ( OV) signal (Delta T-tot similar or equal to 2: 6 mu K). On scales beyond l similar or equal to 4000 the total Doppler signal is dominated by kSZ/ OV, but the patchy signal can contribute up to 30% to the power spectrum. The effect of patchy reionization is largest on scales on which the primordial CMB anisotropies dominate. Ignoring this contribution could lead to significant biases in the determination of cosmological parameters derived from CMB temperature measurements. Improvements in the theoretical modeling of the reionization epoch will become increasingly important to interpret the results of upcoming experiments.