Detectability of the 21 cm-CMB cross-correlation from the EoR

TL;DR

This paper analyzes the potential to detect the cross-correlation between 21-cm line fluctuations and CMB anisotropies during reionisation, assessing signal detectability with current and future radio telescopes.

Contribution

It provides an analytical calculation of the 21-cm and CMB cross-correlation signal and evaluates its detectability with Planck, LOFAR, MWA, and SKA.

Findings

Detection of cross-correlation with CMB polarisation is feasible with SKA.

Instant reionisation produces a detectable cross-correlation signal.

Detection with current instruments like LOFAR is challenging.

Abstract

The 21-cm line fluctuations and the cosmic microwave background (CMB) are powerful probes of the epoch of reionisation of the universe. We study the potential of the cross-correlation between 21-cm line fluctuations and CMB anisotropy to obtain further constraints on the reionisation history. We compute analytically the 21-cm cross-correlation with the CMB temperature anisotropy and polarisation, and we calculate the signal-to-noise (SN) ratio for its detection with Planck together with LOFAR, MWA and SKA. We find, on the one hand, that the 21-cm cross-correlation signal with CMB polarisation from the instant reionisation can be detected with an SN ratio of $\sim 1$ for LOFAR and $\sim 10$ for SKA. On the other hand, we confirm that the detection of the 21-cm cross-correlation with CMB polarisation is practically infeasible.