A cross-bispectrum estimator for CMB-HI intensity mapping correlations

2023/11/10 by Kavilan Moodley, Warren Naidoo, Moodley, Kavilan +5 · 2 citations
Computer Science · Physics and Astronomy · #Adaptive optics and wavefront sensing #Astronomy and Astrophysical Research #Blind Source Separation Techniques #Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences

paper · pdf · doi:10.48550/arxiv.2311.05904

openalex publication_date 2023/11/10 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28

Abstract

Intensity mapping of 21cm emission from neutral hydrogen promises to be a powerful probe of large-scale structure in the post-reionisation epoch. However, HI intensity mapping (IM) experiments will suffer the loss of long-wavelength line-of-sight HI modes in the foreground subtraction process. This significantly reduces HI IM cross-correlations with projected large-scale structure tracers, such as CMB secondary anisotropies. Here we propose a cross-bispectrum estimator, B^ κδT₂₁ δT₂₁, to recover the cross-correlation of the HI IM field, δT₂₁, with the CMB lensing field, κ, constructed by correlating the position-dependent HI power spectrum with the mean overdensity traced by CMB lensing. We study the cross-bispectrum estimator in the squeezed limit and forecast its detectability based on HI IM measurements from HIRAX and CMB lensing measurements from Advanced ACT. We find that B^ κδT₂₁δT₂₁, in combination with the HI IM and CMB lensing auto-spectra, can place sub-percent constraints on the growth rate of fluctuations, f, and the small scale amplitude of fluctuations, σ₈. The cross-bispectrum, in combination with the auto-spectra and Planck priors, improves dark energy constraints to 0.025 on w₀ and 0.11 on w_a for flat models. These results are robust to HI foreground removal because they derive from small-scale HI modes. The HI-CMB lensing cross-bispectrum thus provides a novel way to recover HI correlations with CMB lensing and constrain cosmological parameters at a level that is competitive with next-generation galaxy redshift surveys. As a striking example of this, we find a tight constraint of 27.8 meV (29.0 meV) on the sum of neutrino masses, while varying all redshift and standard cosmological parameters within a flat ΛCDM (w₀w_aCDM) model.

Cited by

• Tracing Large Scale Structure Morphology with Multiwavelength Line Intensity Maps
• Direct correlation of line intensity mapping and CMB lensing from evolution along the lightcone

Related

• Detectability of CMB Weak Lensing and HI Cross Correlation and constraints on cosmological parameters
• The feasibility of weak lensing and 21cm intensity mapping cross-correlation measurements
• Probing the HI distribution at small scales using 21-cm Intensity Mapping at large scales
• Investigating cross-correlations between cosmic microwave background lensing and 21 cm intensity mapping
• Unveiling dark energy properties with high-sensitivity cross-correlations of neutral hydrogen intensity mapping and galaxy surveys