Prospects for ${\rm kSZ^2}$-${\rm 21cm^2}$ Cross-Correlations during Reionization
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| Format: | Preprint |
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2025
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| _version_ | 1866909535779684352 |
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| author | Zhou, Meng La Plante, Paul Lidz, Adam Mao, Yi Ma, Yin-Zhe |
| author_facet | Zhou, Meng La Plante, Paul Lidz, Adam Mao, Yi Ma, Yin-Zhe |
| contents | The 21\,cm line and the patchy kinetic Sunyaev-Zel'dovich (kSZ) effect are promising and complementary probes of the Epoch of Reionization (EoR). A challenge for cross-correlating these two signals is that foreground avoidance or removal algorithms applied to the 21\,cm data inevitably sacrifice Fourier modes with long wavelengths along the line-of-sight (i.e., low-$k_\parallel$ modes), yet \textit{only} these same modes contribute to the kSZ signal. Here we show that a suitable kSZ$^2$ $\times$ 21\,cm$^2$ cross-correlation statistic nevertheless remains non-vanishing, even after filtering out the corrupted low-$k_\parallel$ Fourier modes from the 21\,cm data. We simulate the kSZ$^2$ $\times$ 21\,cm$^2$ cross-correlation signal across reionization-era redshifts and find distinctive redshift evolution. This signal peaks early in the reionization history, when the volume-averaged fraction is around $0.1 \lesssim x_\mathrm{HII} \lesssim 0.2$, after which it changes sign and reaches a minimum near reionization's midpoint ($x_\mathrm{HII} \sim 0.5$), while the signal gradually vanishes as reionization completes. These trends appear generic across three simulated models which differ in their reionization histories. We forecast the detectability of the kSZ$^2$ $\times$ 21\,cm$^2$ cross-power spectrum for the HERA and SKA1-Low 21\,cm experiments in combination with current and next-generation CMB surveys including the Simons Observatory, CMB-S4, and CMB-HD. We find that a high-significance detection ($\mathrm{S/N} \gtrsim 5σ$) is possible with SKA1-Low and CMB-S4. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2503_09462 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Prospects for ${\rm kSZ^2}$-${\rm 21cm^2}$ Cross-Correlations during Reionization Zhou, Meng La Plante, Paul Lidz, Adam Mao, Yi Ma, Yin-Zhe Cosmology and Nongalactic Astrophysics The 21\,cm line and the patchy kinetic Sunyaev-Zel'dovich (kSZ) effect are promising and complementary probes of the Epoch of Reionization (EoR). A challenge for cross-correlating these two signals is that foreground avoidance or removal algorithms applied to the 21\,cm data inevitably sacrifice Fourier modes with long wavelengths along the line-of-sight (i.e., low-$k_\parallel$ modes), yet \textit{only} these same modes contribute to the kSZ signal. Here we show that a suitable kSZ$^2$ $\times$ 21\,cm$^2$ cross-correlation statistic nevertheless remains non-vanishing, even after filtering out the corrupted low-$k_\parallel$ Fourier modes from the 21\,cm data. We simulate the kSZ$^2$ $\times$ 21\,cm$^2$ cross-correlation signal across reionization-era redshifts and find distinctive redshift evolution. This signal peaks early in the reionization history, when the volume-averaged fraction is around $0.1 \lesssim x_\mathrm{HII} \lesssim 0.2$, after which it changes sign and reaches a minimum near reionization's midpoint ($x_\mathrm{HII} \sim 0.5$), while the signal gradually vanishes as reionization completes. These trends appear generic across three simulated models which differ in their reionization histories. We forecast the detectability of the kSZ$^2$ $\times$ 21\,cm$^2$ cross-power spectrum for the HERA and SKA1-Low 21\,cm experiments in combination with current and next-generation CMB surveys including the Simons Observatory, CMB-S4, and CMB-HD. We find that a high-significance detection ($\mathrm{S/N} \gtrsim 5σ$) is possible with SKA1-Low and CMB-S4. |
| title | Prospects for ${\rm kSZ^2}$-${\rm 21cm^2}$ Cross-Correlations during Reionization |
| topic | Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2503.09462 |