The Thermal Sunyaev-Zel'dovich Effect from the Epoch of Reionization

TL;DR

This paper investigates the contribution of the Epoch of Reionization to the thermal Sunyaev-Zel'dovich effect using advanced simulations, revealing it can significantly impact measurements at small scales and may contaminate signals in future observations.

Contribution

The study provides the first detailed simulation-based analysis of the tSZ signal from the Reionization Epoch, highlighting its potential importance for future CMB experiments.

Findings

Reionization contributes about 1% to the tSZ power spectrum at current experimental scales.

The quadratic Doppler effect adds roughly 10% to the tSZ signal during reionization.

At smaller scales, the reionization tSZ signal can dominate, affecting future measurements.

Abstract

The thermal Sunyaev-Zel'dovich (tSZ) effect arises from inverse Compton scattering of low energy photons onto thermal electrons, proportional to the integrated electron pressure, and is usually observed from galaxy clusters. However, we can expect that the Epoch of Reionization (EoR) also contributes to this signal, but that contribution has not been previously evaluated. In this work we analyse a suite of fully-coupled radiation-hydrodynamics simulations based on RAMSES-CUDATON to calculate and study the tSZ signal from the Reionization Epoch. We construct lightcones of the electron pressure in the intergalactic medium for $6<z$ 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 ($\ell\sim10^3-10^4$), we find that the tSZ signal power spectrum from reionization contributes at roughly a percent level compared to the current templates, with the quadratic Doppler effect contributing an additional $\sim10\%$ 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.