The HI intensity mapping bispectrum including observational effects

TL;DR

This paper models the HI intensity mapping bispectrum including observational effects like foreground contamination and beam effects, validated with simulations, to improve analysis of large-scale structure surveys.

Contribution

It introduces a comprehensive model of the HI IM bispectrum that accounts for observational effects, validated with simulations, enhancing the analysis of large-scale structure data.

Findings

Foreground removal reduces bispectrum S/N by 8%

Beam effects reduce bispectrum S/N by 62%

Models fit simulation data well with chi-squared near 1

Abstract

The bispectrum is a 3-point statistic with the potential to provide additional information beyond power spectra analyses of survey datasets. Radio telescopes which broadly survey the 21cm emission from neutral hydrogen (HI) are a promising way to probe LSS and in this work we present an investigation into the HI intensity mapping (IM) bispectrum using simulations. We present a model of the redshift space HI IM bispectrum including observational effects from the radio telescope beam and 21cm foreground contamination. We validate our modelling prescriptions with measurements from robust IM simulations, inclusive of these observational effects. Our foreground simulations include polarisation leakage, on which we use a Principal Component Analysis cleaning method. We also investigate the effects from a non-Gaussian beam including side-lobes. For a MeerKAT-like single-dish IM survey at $z=0.39$, we find that foreground removal causes a 8% reduction in the equilateral bispectrum's signal-to-noise ratio $S/N$, whereas the beam reduces it by 62%. We find our models perform well, generally providing $\chi^2_\text{dof}\sim 1$, indicating a good fit to the data. Whilst our focus is on post-reionisation, single-dish IM, our modelling of observational effects, especially foreground removal, can also be relevant to interferometers and reionisation studies.