A cross-correlation study between the cosmological 21 cm signal and the kinetic Sunyaev-Zel'dovich effect

The Universe's Epoch of Reionization 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 – produced by the scattering of cosmic microwave background (CMB) photons off free electrons produced during the reionization process – and the cosmological 21 cm 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 100 h−1 Mpc scale N-body simulations with radiative transfer. In essence, we find that the two probes anticorrelate. The significance of the anticorrelation 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.