The correlation of high-redshift galaxies with the thermal Sunyaev-Zel'dovich effect traces reionization

TL;DR

This paper proposes using the cross-correlation of high-redshift galaxies with the thermal Sunyaev-Zel'dovich effect maps as a new method to investigate the reionization history of the universe, leveraging upcoming large surveys and simulations.

Contribution

It introduces a novel approach to probe reionization through galaxy-tSZ cross-correlation, combining simulations and forecasted survey data to assess detectability.

Findings

High-redshift galaxies are correlated with tSZ signals from reionization.

Cross-spectra contain information about reionization history and bubble sizes.

Detection is challenging due to low signal amplitude and low-redshift contamination.

Abstract

We explore a potential new probe of reionization: the cross-correlation of high-redshift galaxies with maps of the thermal Sunyaev-Zel'dovich (tSZ) effect. We consider two types of high redshift galaxies: Lyman break galaxies (LBGs) and Lyman-$\alpha$ emitters (LAEs). LBGs and LAEs will be detected in large numbers at high redshift ($z \approx$ 4 to 7) by ongoing and future surveys. We consider a LBG sample like that expected from the The Rubin Observatory Legacy Survey of Space and Time (LSST), and a selection of LAEs modelled after the Subaru SILVERRUSH program, but covering a much larger sky fraction. The tSZ effect is sensitive to a line-of-sight integral of the ionized gas pressure, and can be measured across large patches of the sky using multi-frequency CMB surveys. We consider forecast tSZ maps from CMB Stage 4 and more futuristic observations. Using a suite of hydrodynamical simulations, we show that the high-redshift galaxies are correlated with the tSZ signal from reionization, with cross-power amplitude of order $10^{-15}$ at $\ell \sim 1000$. The cross-spectra between LBGs/LAEs with tSZ maps contain information about the reionization history of the Universe, such as the distribution of bubble sizes, and could in principle be used to directly measure the timing of reionization. The amplitude of the signal is small, however, and its detectability is hindered by low-redshift contributions to tSZ maps and by instrumental noise. If the the low-redshift contribution to the observed tSZ signal is suppressed by masking of massive halos, a combination of overlapping futuristic CMB and galaxy surveys could potentially probe this signal.