Cross-correlation Study between the Cosmological 21-cm Signal and the kinetic Sunyaev-Zel'dovich effect

TL;DR

This study investigates the cross-correlation between the cosmological 21-cm signal and the kinetic Sunyaev-Zel'dovich effect during reionization, revealing an anti-correlation that is obscured by primary CMB fluctuations.

Contribution

It presents the first detailed simulation-based analysis of the cross-correlation between 21-cm and kSZ signals, accounting for realistic reionization histories and CMB noise.

Findings

The 21-cm and kSZ signals anti-correlate during reionization.

Extended reionization histories produce a stronger anti-correlation.

Primary CMB fluctuations dominate noise, masking the cross-correlation signal.

Abstract

The Universe's Epoch of Reionization (EoR) can be studied using a number of observational probes that provide complementary or corroborating information. Each of these probes suffers from its own systematic and statistical uncertainties. It is therefore useful to consider the mutual information that these data sets contain. In this paper we present a cross-correlation study between the kinetic Sunyaev-Zel'dovich effect (kSZ) -- produced by the scattering of CMB photons off free electrons produced during the reionization process -- and the cosmological 21cm signal -- which reflects the neutral hydrogen content of the Universe, as a function of redshift. The study is carried out using a simulated reionization history in 100Mpc/h scale N-body simulations with radiative transfer. In essence we find that the two probes anti-correlate. The significance of the anti-correlation signal depends on the extent of the reionization process, wherein extended histories result in a much stronger signal compared to instantaneous cases. Unfortunately however, once the primary CMB fluctuations are included into our simulation they serve as a source of large correlated noise that renders the cross-correlation signal insignificant, regardless of the reionization scenario.