Papers › Prospects for kSZ²-21cm² Cross-Correlations during Reionization
Prospects for kSZ²-21cm² Cross-Correlations during Reionization
Meng Zhou, Paul La Plante, Adam Lidz, Yi Mao, Yin-Zhe Ma
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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_∥ modes), yet \textit{only} these same modes contribute to the kSZ signal. Here we show that a suitable kSZ² × 21\,cm² cross-correlation statistic nevertheless remains non-vanishing, even after filtering out the corrupted low-k_∥ Fourier modes from the 21\,cm data. We simulate the kSZ² × 21\,cm² 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 ≲x_(HII) ≲0.2, after which it changes sign and reaches a minimum near reionization's midpoint (x_(HII) ∼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 kSZ² × 21\,cm² 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 (S/N ≳5σ) is possible with SKA1-Low and CMB-S4.
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