Parametrizing the Reionization History with the Redshift Midpoint, Duration, and Asymmetry

TL;DR

This paper introduces a new parametrization method for the reionization history using midpoint, duration, and asymmetry parameters, enabling precise comparisons with observations and simulations.

Contribution

It presents a flexible analytical approach to model reionization history that matches simulation results and improves parameter-space studies.

Findings

Matches theoretical reionization models with high accuracy

Limits on differences in key reionization observables

Enables self-consistent constraints from multiple data sources

Abstract

A new parametrization of the reionization history is presented to facilitate robust comparisons between different observations and with theory. The evolution of the ionization fraction with redshift can be effectively captured by specifying the midpoint, duration, and asymmetry parameters. Lagrange interpolating functions are then used to construct analytical curves that exactly fit corresponding ionization points. The shape parametrizations are excellent matches to theoretical results from radiation-hydrodynamic simulations. The comparative differences for reionization observables are: ionization fraction $|\Delta x_\text{i}| \lesssim 0.03$, 21cm brightness temperature $|\Delta T_\text{b}| \lesssim 0.7\, \text{mK}$, Thomson optical depth $|\Delta \tau| \lesssim 0.001$, and patchy kinetic Sunyaev-Zel'dovich angular power $|\Delta D_\ell | \lesssim 0.1\, \mu\text{K}^2$. This accurate and flexible approach will allow parameter-space studies and self-consistent constraints on the reionization history from 21cm, CMB, and high-redshift galaxies and quasars.