On the influence of X-ray galaxy clusters in the fluctuations of the cosmic microwave background

Abstract

The negative evolution found in X-ray clusters of galaxies limits the amount of hot gas available for the inverse Compton scattering of the cosmic microwave background (the Sunyaev-Zel'dovich effect). By the use of a parametrization of the X-ray luminosity function and its evolution in terms of a coalescence model (as presented in the analysis of a flux-limited X-ray cluster sample by Edge et al.), as well as a simple virialized structure for the clusters (which requires a gas-to-total-mass fraction ≳0.1 in order to reproduce observed properties of nearby clusters), we show that the Compton distortion y parameter is about two orders of magnitude below the current FIRAS upper limits. Concerning the anisotropics imprinted on arcmin scales, they are dominated by the hottest undetected objects. We show that they are negligible (δT/T≲ 10-7) at wavelengths λ ≳ 1 mm. At shorter wavelengths, they become more important (ΔT/T∼ 10-6 at λ ∼0.3 mm), but in fact most clusters will produce an isolated and detectable feature in sky maps. After removal of these signals, the fluctuations imprinted by the remaining clusters on the residual radiation are much smaller than 10-6. The conclusion is that X-ray clusters can be ignored as sources of cosmic microwave background fluctuations.