Models of the Cosmological 21 cm Signal from the Epoch of Reionization Calibrated with Lyman-alpha and CMB Data

TL;DR

This paper uses high-resolution simulations calibrated with Lyman-alpha and CMB data to predict the 21 cm signal during reionization, assessing its observability and the impact of self-shielded gas on the power spectrum.

Contribution

It provides new, calibrated models of the 21 cm signal from reionization, predicting observable fluctuations and quantifying the effect of self-shielded gas on the power spectrum.

Findings

Predicted 21 cm brightness temperature variance of 10-20 mK^2 at z=7-10.

Models distinguishable by LOFAR, HERA, SKA1 at their design sensitivities.

Including self-shielded gas reduces large-scale 21 cm power by about 30%.

Abstract

We present here 21 cm predictions from high dynamic range simulations for a range of reionization histories that have been tested against available Lyman-alpha and CMB data. We assess the observability of the predicted spatial 21 cm fluctuations by ongoing and upcoming experiments in the late stages of reionization in the limit in which the hydrogen spin temperature is significantly larger than the CMB temperature. Models consistent with the available Lyman-alpha data and CMB measurement of the Thomson optical depth predict typical values of 10--20 mK^2 for the variance of the 21 cm brightness temperature at redshifts z=7--10 at scales accessible to ongoing and upcoming experiments (k < 1 h/cMpc). This is only a factor of a few below the sensitivity claimed to have been already reached by ongoing experiments in the signal rms value. Our different models for the reionization history make markedly different predictions for the redshift evolution and thus frequency dependence of the 21 cm power spectrum and should be easily discernible by LOFAR (and later HERA and SKA1) at their design sensitivity. Our simulations have sufficient resolution to assess the effect of high-density Lyman limit systems that can self-shield against ionizing radiation and stay 21 cm bright even if the hydrogen in their surroundings is highly ionized. Our simulations predict that including the effect of the self-shielded gas in highly ionized regions reduces the large scale 21 cm power by about 30%.