Reionization inference from the CMB optical depth and E-mode polarization power spectra

Abstract

The Epoch of Reionization (EoR) depends on the complex astrophysics governing the birth and evolution of the first galaxies and structures in the intergalactic medium. EoR models rely on cosmicmicrowave background (CMB) observations, and in particular the large-scale E-mode polarization power spectra (EE PS), to help constrain their highly uncertain parameters. However, rather than directly forward-modelling the EE PS, most EoR models are constrained using a summary statistic - the Thompson scattering optical depth, τe. Compressing CMB observations to τerequires adopting a basis set for the EoR history. The common choice is the unphysical, redshift-symmetric hyperbolic tangent (tanh) functio..