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

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 $k_1\lesssim 0.1{\mathrm{Mpc}}^{-1}$ 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 $k_1\sim 0.2{\mathrm{Mpc}}^{-1}$, 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, $k_1\lesssim 0.8{\mathrm{Mpc}}^{-1}$. 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.

Accepted for publication in MNRAS, 12 pages, 13 figures

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