21cm-line bispectrum as method to probe Cosmic Dawn and Epoch of Reionization

TL;DR

This paper explores the 21cm-line bispectrum as a novel method to analyze non-Gaussian features in the 21cm signal, providing insights into the astrophysical processes during the Cosmic Dawn and Epoch of Reionization.

Contribution

It introduces a detailed analysis of the 21cm bispectrum's properties and component contributions, enhancing the understanding of IGM evolution during early cosmic epochs.

Findings

Different components of the bispectrum show characteristic scale-dependent features.

The bispectrum's shape and redshift dependence reveal detailed astrophysical effects.

Combining bispectrum analysis with power spectrum and skewness improves IGM diagnostics.

Abstract

Redshifted 21cm signal is a promising tool to investigate the state of intergalactic medium (IGM) in the Cosmic Dawn (CD) and Epoch of Reionization(EoR). In our previous work (Shimabukuro et al 2015), we studied the variance and skewness to give a clear interpretation of 21cm power spectrum and found that skewness is a good indicator of the epoch when X-ray heating becomes effective. Thus, the non-Gaussian feature of the spatial distribution of the 21cm signal is expected to be useful to investigate the astrophysical effects in the CD and EoR. In this paper, in order to investigate such a non-Gaussian feature in more detail, we focus on the bispectrum of the 21cm signal. It is expected that the 21cm brightness temperature bispectrum is produced by non-gaussianity due to the various astrophysical effects such as Wouthysen-Field (WF) effect, X-ray heating and reionization. We study the various properties of 21cm bispectrum such as scale dependence, shape dependence and redshift evolution. And also we study the contribution from each component of 21cm bispectrum. We find that the contribution from each component has characteristic scale-dependent feature, and it is expected that we could obtain more detailed information on the IGM in the CD and EoR by using the 21cm bispectrum in the future experiments, combined with the power spectrum and skewness.