Detecting the non-Gaussianity of the 21-cm signal during reionisation with the Wavelet Scattering Transform

TL;DR

This paper introduces a Wavelet Scattering Transform-based method to detect non-Gaussian features in 21-cm signals from the Epoch of Reionisation, outperforming traditional power spectrum analysis in noisy observational data.

Contribution

It presents a novel application of the Wavelet Scattering Transform to extract non-Gaussian information from 21-cm images, enhancing detection capabilities during reionisation.

Findings

Detection of non-Gaussian features at 150 and 177 MHz.

Robustness of the method against statistical noise.

Potential for improved 21-cm signal characterization.

Abstract

Detecting the 21-cm hyperfine transition from neutral hydrogen in the intergalactic medium is our best probe for understanding the astrophysical processes driving the Epoch of Reionisation (EoR). The primary means for a detection of this 21-cm signal is through a statistical measurement of the spatial fluctuations using the 21-cm power spectrum (PS). However, the 21-cm signal is non-Gaussian meaning the PS, which only measures the Gaussian fluctuations, is sub-optimal for characterising all of the available information. The upcoming Square Kilometre Array (SKA) will perform a deep, 1000 hr observation over 100 deg$.^{2}$ specifically designed to recover direct images of the 21-cm signal. In this work, we use the Wavelet Scattering Transform (WST) to extract the non-Gaussian information directly from these two-dimensional images of the 21-cm signal. The key advantage of the WST is its stability with respect to statistical noise for measuring non-Gaussian information, unlike the bispectrum whose statistical noise diverges. We introduce a novel method to isolate this non-Gaussian information from mock 21-cm images and demonstrate its detection at 150 (177)~MHz ($z\sim8.5$ and $\sim7$) for a fiducial model with signal-to-noise of $\sim$5~(8) assuming perfect foreground removal and $\sim2$~(3) assuming foreground wedge avoidance.