On the spin-temperature evolution during the epoch of reionization

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.

15 pages, 18 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society

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• LOFAR: The LOw-Frequency ARray
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• Light cone effect on the reionization 21-cm power spectrum
• Constraining the intergalactic medium at $z\approx$ 9.1 using LOFAR Epoch of Reionization observations
• Probing reionization with LOFAR using 21-cm redshift space distortions
• Constraining the state of the intergalactic medium during the Epoch of Reionization using MWA 21-cm signal observations
• 21-cm signal from cosmic dawn - II: Imprints of the light-cone effects
• Photon number conservation and the large-scale 21 cm power spectrum in semi-numerical models of reionization
• Imaging neutral hydrogen on large-scales during the Epoch of Reionization with LOFAR
• Background reionization history from omniscopes
• Redshifted 21-cm bispectrum II: Impact of the spin temperature fluctuations and redshift space distortions on the signal from the Cosmic Dawn
• LOFAR insights into the epoch of reionization from the cross power spectrum of 21cm emission and galaxies
• Studying Cosmic Dawn using redshifted HI 21-cm signal: A brief review
• A Halo Model Approach to the $21\mathrm{cm}$ and $\mathrm{Ly}\alpha$ Cross-correlation
• Constraints on the state of the IGM at $z\sim 8-10$ using redshifted 21-cm observations with LOFAR
• 21-cm signatures of residual HI inside cosmic HII regions during reionization
• Probing the intergalactic medium during the Epoch of Reionization using 21-cm signal power spectra
• Measuring the reionization 21 cm fluctuations using clustering wedges