The Epoch of Reionization 21-cm Bispectrum: The impact of light-cone effects and detectability

TL;DR

This study analyzes the 21-cm bispectrum during the Epoch of Reionization, focusing on light-cone effects and detection prospects with SKA-Low, highlighting the significance of squeezed triangle configurations for measurement.

Contribution

It introduces a new optimized bispectrum estimation method and assesses the impact of light-cone effects on bispectrum detectability with future radio telescopes.

Findings

Light-cone effects are significant on large scales, especially for squeezed triangles.

A 3-sigma detection is feasible around k ~ 0.2 Mpc^{-1} for all triangle shapes.

Squeezed triangles can achieve over 5-sigma significance across a wide range of scales.

Abstract

We study the spherically averaged bispectrum of the 21-cm signal from the Epoch of Reionization (EoR). This metric provides a quantitative measurement of the level of non-Gaussianity of the signal which is expected to be high. We focus on the impact of the light-cone effect on the bispectrum and its detectability with the future SKA-Low telescope. Our investigation is based on a single reionization light-cone model and an ensemble of 50 realisations of the 21-cm signal to estimate the cosmic variance errors. We calculate the bispectrum with a new, optimised direct estimation method, DviSukta which calculates the bispectrum for all possible unique triangles. We find that the light-cone effect becomes important on scales $k_1 \lesssim 0.1\,{\rm Mpc}^{-1}$ where for most triangle shapes the cosmic variance errors dominate. Only for the squeezed limit triangles, the impact of the light-cone effect exceeds the cosmic variance. Combining the effects of system noise and cosmic variance we find that $\sim 3\sigma$ detection of the bispectrum is possible for all unique triangle shapes around a scale of $k_1 \sim 0.2\,{\rm Mpc}^{-1}$, and cosmic variance errors dominate above and noise errors below this length scale. Only the squeezed limit triangles are able to achieve a more than $5\sigma$ significance over a wide range of scales, $k_1 \lesssim 0.8\,{\rm Mpc}^{-1}$. Our results suggest that among all the possible triangle combinations for the bispectrum, the squeezed limit one will be the most measurable and hence useful.