Probing the large-scale structure with 21cm-galaxy cross-bispectrum: Estimates from simulations and forecasts for upcoming cosmological surveys
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| Natura: | Preprint |
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2026
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| author | Noble, Leon Majumdar, Suman Viel, Matteo Fontanot, Fabio De Lucia, Gabriella Shaw, Abinash Kumar Spinelli, Marta Kamran, Mohd Xie, Lizhi Hirschmann, Michaela |
| author_facet | Noble, Leon Majumdar, Suman Viel, Matteo Fontanot, Fabio De Lucia, Gabriella Shaw, Abinash Kumar Spinelli, Marta Kamran, Mohd Xie, Lizhi Hirschmann, Michaela |
| contents | The redshifted 21cm signal from the post-reionization epoch is highly non-Gaussian; thus, higher-order statistics, such as the bispectrum, are required to extract this non-Gaussian information. However, high-signal-to-noise ratio detection of the 21cm auto-bispectrum will be hindered by the presence of residual systematics. Cross-correlating the 21cm signal with galaxies offers a promising path to suppress this uncertainty from residual systematics and potentially increase the signal-to-noise ratio. We present a comprehensive analysis of the HI-galaxy cross-bispectrum using the predictions of theoretical galaxy evolution models defined on large cosmological volumes. Our analysis includes the cross-bispectrum for different triangle sizes and shapes, as well as for different combinations of the HI and galaxy fields. We forecast the detectability of the 21cm-galaxy cross-bispectrum at redshift $z\approx1$ with Euclid-like galaxy survey and SKA-Mid observations in both interferometric and single-dish modes of survey. We find that the 21cm-galaxy cross-bispectrum shows enhanced detectability compared to the 21cm auto-bispectrum for all unique triangles in the presence of instrumental noise for observations in interferometric mode. We forecast a 10$σ$ detection of cross-bispectrum for squeezed-limit triangles and a 100$σ$ detection for all shapes combined for scales $0.2~\text{Mpc}^{-1}\leq k_1 \leq 0.9~\text{Mpc}^{-1}$ with 100 hours of SKA-Mid observations per pointing. However, the detectability of the cross-bispectrum for large scales ($k_1 < 0.1~\text{Mpc}^{-1}$), which is accessible with the single-dish mode of survey, is limited by cosmic variance. Our analysis presents a first step towards an end-to-end analysis pipeline for the future observations of the 21cm-galaxy cross-bispectrum. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2604_15440 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Probing the large-scale structure with 21cm-galaxy cross-bispectrum: Estimates from simulations and forecasts for upcoming cosmological surveys Noble, Leon Majumdar, Suman Viel, Matteo Fontanot, Fabio De Lucia, Gabriella Shaw, Abinash Kumar Spinelli, Marta Kamran, Mohd Xie, Lizhi Hirschmann, Michaela Cosmology and Nongalactic Astrophysics The redshifted 21cm signal from the post-reionization epoch is highly non-Gaussian; thus, higher-order statistics, such as the bispectrum, are required to extract this non-Gaussian information. However, high-signal-to-noise ratio detection of the 21cm auto-bispectrum will be hindered by the presence of residual systematics. Cross-correlating the 21cm signal with galaxies offers a promising path to suppress this uncertainty from residual systematics and potentially increase the signal-to-noise ratio. We present a comprehensive analysis of the HI-galaxy cross-bispectrum using the predictions of theoretical galaxy evolution models defined on large cosmological volumes. Our analysis includes the cross-bispectrum for different triangle sizes and shapes, as well as for different combinations of the HI and galaxy fields. We forecast the detectability of the 21cm-galaxy cross-bispectrum at redshift $z\approx1$ with Euclid-like galaxy survey and SKA-Mid observations in both interferometric and single-dish modes of survey. We find that the 21cm-galaxy cross-bispectrum shows enhanced detectability compared to the 21cm auto-bispectrum for all unique triangles in the presence of instrumental noise for observations in interferometric mode. We forecast a 10$σ$ detection of cross-bispectrum for squeezed-limit triangles and a 100$σ$ detection for all shapes combined for scales $0.2~\text{Mpc}^{-1}\leq k_1 \leq 0.9~\text{Mpc}^{-1}$ with 100 hours of SKA-Mid observations per pointing. However, the detectability of the cross-bispectrum for large scales ($k_1 < 0.1~\text{Mpc}^{-1}$), which is accessible with the single-dish mode of survey, is limited by cosmic variance. Our analysis presents a first step towards an end-to-end analysis pipeline for the future observations of the 21cm-galaxy cross-bispectrum. |
| title | Probing the large-scale structure with 21cm-galaxy cross-bispectrum: Estimates from simulations and forecasts for upcoming cosmological surveys |
| topic | Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2604.15440 |