Redshifted 21cm bispectrum  I. Impact of the redshift space distortions on the signal from the Epoch of Reionization
Abstract
The bispectrum can quantify the nonGussianity present in the redshifted 21cm signal produced by the neutral hydrogen ( $\rm {H \small {I}}$ ) during the Epoch of Reionization (EoR). Motivated by this, we perform a comprehensive study of the EoR 21cm bispectrum using simulated signals. Given a model of reionization, we demonstrate the behaviour of the bispectrum for all unique triangles in k space. For ease of identification of the unique triangles we parametrize the ktriangle space with two parameters, namely the ratio of the two arms of the triangle (n = k_{2}/k_{1}) and the cosine of the angle between them (cos θ). Furthermore, for the first time we quantify the impact of the redshift space distortions (RSD) on the spherically averaged EoR 21cm bispectrum in the entire unique triangle space. We find that the real space signal bispectra for small and intermediate k_{1}triangles ( $k_1 \le 0.6 \, \, {\rm Mpc}^{1}$ ) is negative in most of the unique triangle space. It takes a positive sign for squeezed, stretched, and linear k_{1}triangles, specifically for large k_{1} values ( $k_1 \ge 0.6 \, \, {\rm Mpc}^{1}$ ). The RSD affects both the sign and magnitude of the bispectra significantly. It changes (increases/decreases) the magnitude of the bispectra by $50\!\!100{{\ \rm per\ cent}}$ without changing its sign (mostly) during the entire period of the EoR for small and intermediate k_{1}triangles. For larger k_{1}triangles, RSD affects the magnitude by $100\!\!200{{\ \rm per\ cent}}$ and also flips the sign from negative to positive. We conclude that it is important to take into account the impact of RSD for a correct interpretation of the EoR 21cm bispectra.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 December 2020
 DOI:
 10.1093/mnras/staa3168
 arXiv:
 arXiv:2007.06584
 Bibcode:
 2020MNRAS.499.5090M
 Keywords:

 methods: numerical;
 dark ages;
 reionization;
 first stars;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 18 pages, 11 figures. Accepted for publication in the MNRAS. Replaced to match the accepted version