Probing Early Phases of the Epoch of Reionization with the kSZ2×21 cm2 Cross-Correlation
Abstract
Observations of the Epoch of Reionization (EoR) provide key insights into the nature of the first luminous sources and the thermal state of the intergalactic medium (IGM). Cross-correlations between the kinetic Sunyaev--Zel'dovich (kSZ) effect and neutral hydrogen (HI) 21-cm emission offer a promising probe of this era, sensitive to both the ionization and thermal histories of the early Universe. We investigate the cross-correlation of the squared kSZ field with the squared 21-cm intensity-mapping field (kSZ2×21cm2) over z≃9--$16$, focusing on the impact of spatial fluctuations in the HI spin temperature. This higher-order statistic avoids line-of-sight cancellations in the kSZ signal, while squaring the 21-cm field enables non-vanishing correlations with pairs of equal and opposite high-k∥ modes accessible outside the foreground wedge. We forecast the cumulative signal-to-noise ratio (S/N) for several combinations of 21-cm and CMB experiments, including realistic instrumental noise. For a fiducial heating history and an optimistic foreground-avoidance scenario (k∥≤0.1 h Mpc−1), we find S/N≃5.89 for SKA-Low AA∗×CMB-HD and ≃3.62 for HERA×CMB-HD. If the foreground wedge extends to the horizon, these decrease to $2.94$ and $2.85$, respectively. Our results demonstrate that kSZ2×21cm2 is sensitive to the thermal evolution of the IGM as well as its ionization structure, providing complementary constraints on the high-redshift thermal and reionization histories.
Related
- Consistently Reproducing Early Galaxy Observations and 21-cm Signal during the Epoch of Reionization
- Square Kilometer Array Synergies for the Epoch of Reionization and Cosmic Dawn
- The multiphase circumgalactic medium in the epoch of reionization: CII and CIV absorbers around [OIII] emitters
- hyprfine: simulating the 21-cm signal from the Dark Ages through to the Epoch of Reionization on a GPU
- Detectability of 21-cm Power Spectra from the Epoch of Reionization using Modern Radio Telescopes
BibTeX
@misc{guo2026probing,
title = {{Probing Early Phases of the Epoch of Reionization with the $\mathrmkSZ^2\times21\,\mathrmcm^2$ Cross-Correlation}},
author = {Wen-Qing Guo and Yin-Zhe Ma and Adam Lidz and Steven Murray and Hemanth Potluri},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.03527},
eprint = {2610.03527},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.03527},
}
RIS
TY - UNPB
TI - Probing Early Phases of the Epoch of Reionization with the kSZ^2×21 cm^2 Cross-Correlation
AU - Wen-Qing Guo
AU - Yin-Zhe Ma
AU - Adam Lidz
AU - Steven Murray
AU - Hemanth Potluri
PY - 2026
DA - 2026/10/02
PB - arXiv
DO - 10.48550/arxiv.2610.03527
UR - https://arxiv.org/abs/2610.03527
AB - Observations of the Epoch of Reionization (EoR) provide key insights into the nature of the first luminous sources and the thermal state of the intergalactic medium (IGM). Cross-correlations between the kinetic Sunyaev--Zel'dovich (kSZ) effect and neutral hydrogen (HI) 21-cm emission offer a promising probe of this era, sensitive to both the ionization and thermal histories of the early Universe. We investigate the cross-correlation of the squared kSZ field with the squared 21-cm intensity-mapping field (kSZ^2×21cm^2) over z≃9--$16$, focusing on the impact of spatial fluctuations in the HI spin temperature. This higher-order statistic avoids line-of-sight cancellations in the kSZ signal, while squaring the 21-cm field enables non-vanishing correlations with pairs of equal and opposite high-k_∥ modes accessible outside the foreground wedge. We forecast the cumulative signal-to-noise ratio (S/N) for several combinations of 21-cm and CMB experiments, including realistic instrumental noise. For a fiducial heating history and an optimistic foreground-avoidance scenario (k_∥≤0.1 h Mpc^−1), we find S/N≃5.89 for SKA-Low AA^∗×CMB-HD and ≃3.62 for HERA×CMB-HD. If the foreground wedge extends to the horizon, these decrease to $2.94$ and $2.85$, respectively. Our results demonstrate that kSZ^2×21cm^2 is sensitive to the thermal evolution of the IGM as well as its ionization structure, providing complementary constraints on the high-redshift thermal and reionization histories.
ER -