On the spin-temperature evolution during the epoch of reionization

TL;DR

This paper extends a reionization simulation algorithm to include self-consistent spin temperature calculations, revealing significant effects on the 21-cm signal at high redshifts, crucial for accurate interpretation of observational data.

Contribution

It introduces a method to incorporate spin temperature coupling effects into reionization simulations, improving the accuracy of 21-cm signal modeling during the epoch of reionization.

Findings

Spin temperature evolution affects the 21-cm signal at redshifts above 10.

Self-consistent modeling alters the interpretation of observational data.

Different reionization sources impact the spin temperature and signal evolution.

Abstract

Simulations estimating the differential brightness temperature of the redshifted 21-cm from the epoch of reionization (EoR) often assume that the spin temperature is decoupled from the background CMB temperature and is much larger than it. Although a valid assumption towards the latter stages of the reionization process, it does not necessarily hold at the earlier epochs. Violation of this assumption will lead to fluctuations in differential brightness temperature that are neither driven by density fluctuations nor by HII regions. Therefore, it is vital to calculate the spin temperature self-consistently by treating the Lyman-alpha and collisional coupling of spin temperature to the kinetic temperature. In this paper we develop an extension to the BEARS algorithm, originally developed to model reionization history, to include these coupling effects. Here we simulate the effect in ionization and heating for three models in which the reionization is driven by stars, miniqsos or a mixture of both.We also perform a number of statistical tests to quantify the imprint of the self-consistent inclusion of the spin temperature decoupling from the CMB. We find that the evolution of the spin temperature has an impact on the measured signal specially at redshifts higher than 10 and such evolution should be taken into account when one attempts to interpret the observational data.