The thermal Sunyaev-Zel’dovich effect from the epoch of reionisation

The thermal Sunyaev-Zel’dovich (tSZ) effect arises from inverse Compton scattering of low energy photons with thermal electrons, and is usually observed in galaxy clusters. During the Epoch of Reionisation (EoR), although the temperature of the ionised intergalactic medium (IGM) is lower, its high density leads to an increased electron pressure which results in a tSZ effect. In order to investigate its strength, we analyse data obtained from fully-coupled radiation-hydrodynamics simulations and construct lightcones of the electron pressure in the IGM during the EoR. These simulations utilise the hybrid CPU-GPU code RAMSES-CUDATON and span the duration of reionisation. We vary the box sizes, star formation parameters and resolutions to investigate how these factors affect the tSZ effect. We produce plots of maps and distributions of the Compton y-parameter, as well as angular power spectra of the tSZ signal, obtained from integrating the lightcones constructed for each simulation. We find that having a high box resolution is important as smaller areas where the temperature is higher are better resolved, leading to higher values of the y-parameter. We estimate the average y-parameter arising from the EoR to be (y) ~ 10-8, making this the first time this value has been calculated from numerical simulations. In the case of the power spectra, on scales probed by current technology, we find that the tSZ signal from the EoR is < 1% of that modelled by cluster templates. Our results suggest that it would be worthwhile to consider the contribution of the EoR to the tSZ effect in the future when more sensitive technologies emerge.