Observing patchy reionization with future CMB polarization experiments

Abstract

We study the signal from patchy reionization in view of the future high accuracy polarization measurements of the Cosmic Microwave Background (CMB). We implement an extraction procedure of the patchy reionization signal analogous to CMB lensing. We evaluate the signal to noise ratio (SNR) for the future Stage IV (S4) CMB experiment. The signal has a broad peak centered on the degree angular scales, with a long tail at higher multipoles. The CMB S4 experiment can effectively constrain the properties of reionization by measuring the signal on degree scales. The signal amplitude depends on the properties of the structure determining the reionization morphology. We describe bubbles having radii distributed log-normally. The expected S/N is sensitive to the mean bubble radius: $\bar{R}=5$ Mpc implies $S/N \approx 4$, $\bar{R}=10$ Mpc implies $S/N \approx 20$. The spread of the radii distribution strongly affects the integrated SNR, that changes by a factor of $10^2$ when $\sigma_{lnr}$ goes from $\ln 2$ to $\ln3$. Future CMB experiments will thus place important constraints on the physics of reionization.