LIMFAST. V. Probing Reionization with the Synergy Between 21 cm and Photometric Galaxy Surveys
Abstract
Cross-correlating the 21\,cm signal from intergalactic neutral hydrogen with the galaxy distribution is a powerful probe of the Epoch of Reionization and the physical mechanisms driving it. While upcoming surveys with the SKA-Low radio telescope and the Roman Space Telescope offer ideal synergies for this measurement, foreground mitigation of 21\,cm data requires exquisite redshift precision of galaxies, effectively excluding the rich photometrically selected samples of Lyman-break galaxies (LBGs) with typical redshift uncertainties σz ≳ 0.1. We overcome this challenge using a squared statistic of the foreground-cleaned 21\,cm signal. Squaring the filtered 21\,cm signal couples surviving high k∥ modes into low k∥ fluctuations accessible to photometric LBG surveys. This higher-order cross-correlation statistic remains measurable even when direct cross-correlations are strongly suppressed. Applying Fisher matrix analysis to this LBG--21\,cm2 cross-correlation signal simulated by the \texttt{LIMFAST} code over 6 ≲ z ≲ 10, we investigate the prospects for constraining EoR physics combining SKA-Low 21\,cm measurements and Roman photometric galaxy samples. For an overlapping survey area covering 10\,deg2, we find that the LBG--21\,cm2 cross-correlation is detectable at high significance across much of the EoR through 1000\,hours of SKA-Low integration with 15\,MHz bandwidth and a Roman photometric galaxy sample from the High-Latitude Wide-Area Survey (HLWAS) reaching mAB,lim=27 and photo-z uncertainties of σz ∼ 0.1--0.3. The characteristic sign evolution of the large-scale cross-power spectrum---driven primarily, though not exclusively, by the evolving neutral fraction---provides strong constraints on the physical parameters governing the ionization and thermal history of the IGM.
Related
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BibTeX
@misc{sun2026limfast,
title = {{LIMFAST. V. Probing Reionization with the Synergy Between 21 cm and Photometric Galaxy Surveys}},
author = {Guochao Sun and Adam Lidz and Tzu-Ching Chang and Claude-André Faucher-Giguère and Steven R. Furlanetto and Aritra Kundu and Jordan Mirocha},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.35957},
eprint = {2609.35957},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.35957},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - LIMFAST. V. Probing Reionization with the Synergy Between 21 cm and Photometric Galaxy Surveys
AU - Guochao Sun
AU - Adam Lidz
AU - Tzu-Ching Chang
AU - Claude-André Faucher-Giguère
AU - Steven R. Furlanetto
AU - Aritra Kundu
AU - Jordan Mirocha
PY - 2026
DA - 2026/09/28
PB - arXiv
DO - 10.48550/arxiv.2609.35957
UR - https://arxiv.org/abs/2609.35957
AB - Cross-correlating the 21\,cm signal from intergalactic neutral hydrogen with the galaxy distribution is a powerful probe of the Epoch of Reionization and the physical mechanisms driving it. While upcoming surveys with the SKA-Low radio telescope and the Roman Space Telescope offer ideal synergies for this measurement, foreground mitigation of 21\,cm data requires exquisite redshift precision of galaxies, effectively excluding the rich photometrically selected samples of Lyman-break galaxies (LBGs) with typical redshift uncertainties σ_z ≳ 0.1. We overcome this challenge using a squared statistic of the foreground-cleaned 21\,cm signal. Squaring the filtered 21\,cm signal couples surviving high k_∥ modes into low k_∥ fluctuations accessible to photometric LBG surveys. This higher-order cross-correlation statistic remains measurable even when direct cross-correlations are strongly suppressed. Applying Fisher matrix analysis to this LBG--21\,cm^2 cross-correlation signal simulated by the \texttt{LIMFAST} code over 6 ≲ z ≲ 10, we investigate the prospects for constraining EoR physics combining SKA-Low 21\,cm measurements and Roman photometric galaxy samples. For an overlapping survey area covering 10\,deg^2, we find that the LBG--21\,cm^2 cross-correlation is detectable at high significance across much of the EoR through 1000\,hours of SKA-Low integration with 15\,MHz bandwidth and a Roman photometric galaxy sample from the High-Latitude Wide-Area Survey (HLWAS) reaching m_AB,lim=27 and photo-z uncertainties of σ_z ∼ 0.1--0.3. The characteristic sign evolution of the large-scale cross-power spectrum---driven primarily, though not exclusively, by the evolving neutral fraction---provides strong constraints on the physical parameters governing the ionization and thermal history of the IGM.
ER -