Paper detail

On the Cluster Physics of Sunyaev-Zel'dovich Surveys I: The Influence of Feedback, Non-thermal Pressure and Cluster Shapes on Y-M Scaling Relations

The utility of large Sunyaev Zel'dovich (SZ) surveys for determining cosmological parameters from cluster abundances is limited by the theoretical uncertainties in the integrated SZ-flux-to-mass relation, Y-M. We explore how non-thermal pressure and the anisotropic shape of the gas distribution of the intracluster medium (ICM) impacts Y-M scaling using a suite of SPH simulations of the cosmic web. We contrast results for models with different treatments of entropy injection and transport, varying radiative cooling, star formation and accompanying supernova feedback, cosmic rays, and energetic feedback from active galactic nuclei (AGN). We find that the gas kinetic-to-thermal pressure ratio from internal bulk motions depends on the cluster mass, and increases in the outer-cluster due to enhanced substructure, as does the asphericity of the ICM gas. With only a ~5-10% correction to projected (observable) ellipticities, we can infer the 3D ellipticities. Our simulated Y-M-slope roughly follows the self-similar prediction, except for a steepening due to a deficit of gas in lower mass clusters at low redshift in our AGN-feedback simulations. AGN feedback enhances slightly the overall Y-M-scatter, from ~11% to ~13%, a reflection of accretion history variations due to cluster merging. If we split the cluster system into lower, middle and upper bands of both P_kin/P_th and long-to-short axis ratio, we find a ~10% effect on Y-M. Identifying observable second parameters related to internal bulk flows and anisotropy for cluster-selection to minimize Y-M scatter in a "fundamental plane" would allow tighter cosmological parameter constraints.