Modal compression of the redshiftspace galaxy bispectrum
Abstract
We extend the modal decomposition method, previously applied to compress the information in the realspace bispectrum, to the anisotropic redshiftspace galaxy bispectrum. In the modal method approach, the bispectrum is expanded on a basis of smooth functions of triangles and their orientations, such that a set of modal expansion coefficients can capture the information in the bispectrum. We assume a reference survey and compute Fisher forecasts for the compressed modal bispectrum and two other basis decompositions of the redshiftspace bispectrum in the literature, one based on (single) spherical harmonics and another based on tripolar spherical harmonics. In each case, we compare the forecasted constraints from the compressed statistic with forecasted constraints from the full, uncompressed bispectrum which includes all triangles and orientations. Our main result is that all three compression methods achieve good recovery of the full information content of the bispectrum, but the modal decomposition approach achieves this the most efficiently: only 14 (42) modal expansion coefficients are necessary to obtain constraints that are within 10 (2) per cent of the full bispectrum result. The next most efficient decomposition is the one based on tripolar spherical harmonics, while the spherical harmonic multipoles are the least efficient.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 August 2022
 DOI:
 10.1093/mnras/stac2313
 arXiv:
 arXiv:2205.04579
 Bibcode:
 2022MNRAS.tmp.2216B
 Keywords:

 Cosmology: theory;
 largescale structure of the Universe;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 17 pages, 5 figures, 2 tables. To be submitted to MNRAS. Comments welcome