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

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 (LC) effect on the bispectrum and its detectability with the future SKA-Low telescope. Our investigation is based on a single reionization LC model and an ensemble of 50 realizations of the 21-cm signal to estimate the cosmic variance errors. We calculate the bispectrum with a new, optimized direct estimation method, DVISUKTA, which calculates the bispectrum for all possible unique triangles. We find that the LC effect becomes important on scales k(1) less than or similar to 0.1 Mpc(-1), where, for most triangle shapes, the cosmic variance errors dominate. Only for the squeezed limit triangles, the impact of the LC effect exceeds the cosmic variance. Combining the effects of system noise and cosmic variance we find that similar to 3 sigma detection of the bispectrum is possible for all unique triangle shapes around a scale of k(1) similar to 0.2 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 5a significance over a wide range of scales, k(1) less than or similar to 0.8 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.

Automated summary

We studied the spherically averaged bispectrum of the 21-cm signal from the Epoch of Reionization and found that the light-cone effect becomes significant on scales less than or similar to 0.1 Mpc(-1), where cosmic variance errors dominate for most triangle shapes. Only for squeezed limit triangles does the impact of the light-cone effect exceed cosmic variance.