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

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.

Published in ApJL, 6 pages, 4 figures, 1 table

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• SCORCH. II. Radiation-Hydrodynamic simulations of reionization with varying radiation escape fractions
• LIMFAST. II. Line Intensity Mapping as a Probe of High-Redshift Galaxy Formation
• Optical depth to reionization from perturbative 21cm clustering
• Probing the intergalactic medium during the Epoch of Reionization using 21-cm signal power spectra
• Hunting Primordial Black Hole Dark Matter in Lyman-$\alpha$ Forest
• The Reionization Parameter Space Consistent with the Thomson Optical Depth from Planck
• Impact of the primordial fluctuation power spectrum on the reionization history