The thermal Sunyaev–Zel’dovich effect from the epoch of reionization

ABSTRACT The thermal Sunyaev–Zel’dovich (tSZ) effect arises from inverse Compton scattering of low energy photons on to thermal electrons, proportional to the integrated electron pressure, and is usually observed from galaxy clusters. We can expect that the epoch of reionization (EoR) also contributes to this signal, but this has not been previously evaluated. In this work, we analyse a suite of fully coupled radiation–hydrodynamics simulations based on ramses-cudaton to study the EoR tSZ signal. We construct lightcones of the electron pressure in the intergalactic medium for $6\lesssim z$ to calculate the resulting Compton y-parameters. We vary the box sizes, resolutions, and star formation parameters to investigate how these factors affect the tSZ effect. We produce plots of maps and distributions of y, as well as angular temperature power spectra of the tSZ signal obtained from integrating the lightcones constructed for each simulation. We find that the tSZ signal from reionization is generally sub-dominant to the post-reionization one at larger scales ($\ell < 10^4$), but can contribute non-trivially and potentially contaminate the measured signals. At scales probed by current experiments like SPT ($\ell \sim 10^3-10^4$), we find that the tSZ signal power spectrum from reionization contributes at roughly a per cent level compared to the current templates, with the quadratic Doppler effect contributing an additional ∼10 per cent to the tSZ signal. At smaller scales the tSZ from reionization peaks and can potentially dominate the total signal and is thus a potentially much more important contribution to take into account in any future, more sensitive experiments.