The Squeezed Bispectrum from CHIME HI Emission and Planck CMB Lensing: Current Sensitivity and Forecasts
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2026
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| author | CHIME Collaboration Chakraborty, Arnab Dobbs, Matt Foreman, Simon Gray, Liam Halpern, Mark Hinshaw, Gary Joseph, Albin MacEachern, Joshua Masui, Kiyoshi W. Mena-Parra, Juan Newburgh, Laura Pinsonneault-Marotte, Tristan Reda, Alex Shaikh, Shabbir Siegel, Seth Wang, Haochen Wulf, Dallas Ahmed, Zeeshan Kokron, Nickolas Schaan, Emmanuel |
| author_facet | CHIME Collaboration Chakraborty, Arnab Dobbs, Matt Foreman, Simon Gray, Liam Halpern, Mark Hinshaw, Gary Joseph, Albin MacEachern, Joshua Masui, Kiyoshi W. Mena-Parra, Juan Newburgh, Laura Pinsonneault-Marotte, Tristan Reda, Alex Shaikh, Shabbir Siegel, Seth Wang, Haochen Wulf, Dallas Ahmed, Zeeshan Kokron, Nickolas Schaan, Emmanuel |
| contents | Line intensity mapping using atomic hydrogen (HI) has the potential to efficiently map large volumes of the universe if the signal can be successfully separated from overwhelmingly bright radio foreground emission. This motivates cross-correlations, to ascertain the cosmological nature of measured HI fluctuations, and to study their connections with galaxies and the underlying matter density field. However, these same foregrounds render the cross-correlation with projected fields such as the lensing of the cosmic microwave background (CMB) difficult. Indeed, the correlated Fourier modes vary slowly along the line of sight, and are thus most contaminated by the smooth-spectrum radio continuum foregrounds. In this paper, we implement a method that avoids this issue by attempting to measure the non-linear gravitational coupling of the small-scale 21cm power from the Canadian Hydrogen Intensity Mapping Experiment (CHIME) with large-scale Planck CMB lensing. This measurement is a position-dependent power spectrum, i.e. a squeezed integrated bispectrum. Using 94 nights of CHIME data between $1.0 < z < 1.3$ and aggressive foreground filtering, we find that the expected signal is five times smaller than the current noise. We forecast that incorporating the additional nights of CHIME data already collected would enable a signal-to-noise ratio of 3, without any further improvements in filtering for foreground cleaning. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2601_03240 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | The Squeezed Bispectrum from CHIME HI Emission and Planck CMB Lensing: Current Sensitivity and Forecasts CHIME Collaboration Chakraborty, Arnab Dobbs, Matt Foreman, Simon Gray, Liam Halpern, Mark Hinshaw, Gary Joseph, Albin MacEachern, Joshua Masui, Kiyoshi W. Mena-Parra, Juan Newburgh, Laura Pinsonneault-Marotte, Tristan Reda, Alex Shaikh, Shabbir Siegel, Seth Wang, Haochen Wulf, Dallas Ahmed, Zeeshan Kokron, Nickolas Schaan, Emmanuel Cosmology and Nongalactic Astrophysics Line intensity mapping using atomic hydrogen (HI) has the potential to efficiently map large volumes of the universe if the signal can be successfully separated from overwhelmingly bright radio foreground emission. This motivates cross-correlations, to ascertain the cosmological nature of measured HI fluctuations, and to study their connections with galaxies and the underlying matter density field. However, these same foregrounds render the cross-correlation with projected fields such as the lensing of the cosmic microwave background (CMB) difficult. Indeed, the correlated Fourier modes vary slowly along the line of sight, and are thus most contaminated by the smooth-spectrum radio continuum foregrounds. In this paper, we implement a method that avoids this issue by attempting to measure the non-linear gravitational coupling of the small-scale 21cm power from the Canadian Hydrogen Intensity Mapping Experiment (CHIME) with large-scale Planck CMB lensing. This measurement is a position-dependent power spectrum, i.e. a squeezed integrated bispectrum. Using 94 nights of CHIME data between $1.0 < z < 1.3$ and aggressive foreground filtering, we find that the expected signal is five times smaller than the current noise. We forecast that incorporating the additional nights of CHIME data already collected would enable a signal-to-noise ratio of 3, without any further improvements in filtering for foreground cleaning. |
| title | The Squeezed Bispectrum from CHIME HI Emission and Planck CMB Lensing: Current Sensitivity and Forecasts |
| topic | Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2601.03240 |