The impact of galaxy formation on the Sunyaev-Zeldovich effect of galaxy clusters

We study the effects of radiative cooling and galaxy formation on the Sunyaev-Zel'dovich (SZ) observable-mass relations using high-resolution cosmological simulations. The simulations of eleven individual clusters spanning a decade in mass are performed with the shock-capturing eulerian adaptive mesh refinement N-body+gasdynamics ART code. To assess the impact of galaxy formation, we compare two sets of simulations performed in the adiabatic regime (without dissipation) and with radiative cooling and several physical processes critical to various aspects of galaxy formation: star formation, metal enrichment and stellar feedback. We show that the SZ signal integrated to sufficiently large fraction of the cluster volume correlates strongly with the enclosed cluster mass, regardless of the details of the cluster physics or dynamical state of the cluster. The slope and redshift evolution of the SZ flux-mass relation are also insensitive to the details of the cluster gas physics, and they are well characterized by the simple self-similar cluster model. While the tightness, slope and redshift evolution are relatively unaffected, we show that the radiative cooling and galaxy formation significantly modify the normalization of the SZ scaling relations. In our simulations, we find that the gas cooling and associated star formation suppress the normalization by ≈30--40%. The effect is due to the decrease in the hot gas fraction, which is offset slightly by the increase in the gas temperature. The baryon dissipation also slightly modifies the cluster mass and affects the normalization by non-negligible amount. Finally, we show that the simulations that include gas cooling and star formation are in good agreement with the recent observational results on the SZ scaling relations obtained using 36 OVRO/BIMA SZ+Chandra X-ray cluster observations, while the simulations neglecting galaxy formation are inconsistent with the observed correlation. The comparison highlights the importance of galaxy formation in theoretical modelling of clusters and shows that the current generation of simulations produce clusters with gross properties quite similar to their observed counterparts.