Observing the Epoch of Reionization with the Cosmic Microwave Background

TL;DR

This paper reviews how the epoch of reionization affects the cosmic microwave background, discussing current constraints, future measurement prospects, and related phenomena like the kinematic Sunyaev-Zel'dovich effect and spectral distortions.

Contribution

It provides a comprehensive review of observational signatures of reionization in the CMB and discusses future measurement forecasts and proposals.

Findings

WMAP and Planck constrain reionization timing via polarization data.

The kSZ effect depends on reionization duration and current measurements are improving.

Future missions aim to measure optical depth with higher precision.

Abstract

We review the observable consequences of the epoch of reionization (EoR) on the cosmic microwave background (CMB), and the resulting constraints on the EoR. We discuss how Thomson scattering with the free electrons produced during EoR equates to an optical depth for CMB photons. The optical depth measurements from the WMAP and Planck satellites, using large-scale CMB polarization power spectra, is one of the few current constraints on the timing of cosmic reionization. We also present forecasts for the precision with which the optical depth will be measured by future satellite missions. Second, we consider the kinematic Sunyaev-Zel'dovich (kSZ) effect, and how the kSZ power spectrum depends on the duration of reionization. We review current measurements of the kSZ power and forecasts for future experiments. Finally, we mention proposals to look for spectral distortions in the CMB that are related to the electron temperature at EoR, and ideas to map the variations in the optical depth across the sky.