The Reionization Parameter Space Consistent with the Thomson Optical Depth from Planck

TL;DR

This study constrains the reionization history parameters using Planck's Thomson optical depth measurements, employing a new parametrization and MCMC analysis to derive limits on reionization timing and shape.

Contribution

It introduces a novel parametrization of reionization history and provides updated constraints on reionization parameters consistent with Planck data.

Findings

Redshift midpoint of reionization: z_{50}=7.66 with uncertainties.

Upper limits on duration: Δ_z<7.5 and asymmetry: A_z<5.3.

Reconstructed ionization fraction is asymmetric with minor early contributions.

Abstract

We study the reionization parameter space consistent with the current measurement of the Thomson optical depth using a new parametrization of the reionization history. The mass-weighted ionization fraction is specified in terms of the redshift midpoint, duration, and asymmetry shape parameters. We perform an MCMC analysis using conservative flat priors and physical constraints. Our analysis yields a redshift midpoint of $z_{50}=7.66\substack{+0.57-0.61}\text{(68%)}\substack{+1.26-1.02}\text{(95%)}$, and upper limits on the duration $\Delta_\text{z} < 7.5$ and asymmetry $A_\text{z}<5.3$ for $\tau = 0.054 \pm 0.007$. The reconstructed mass-weighted ionization fraction $x_\text{i}(z)$ is asymmetric, but early contributions to reionization are minor.