Conduction and Turbulent Mixing in Galaxy Clusters
  We discuss hydrostatic models of galaxy clusters in which heat diffusion balances radiative cooling. We consider two different sources of diffusion, thermal conduction and turbulent mixing, parameterized by dimensionless coefficients, f and alpha_mix, respectively. Models with thermal conduction give reasonably good fits to the density and temperature profiles of several cooling flow clusters, but some clusters require unphysically large values of f>1. Models with turbulent mixing give good fits to all clusters, with reasonable values of alpha_mix ~ 0.01-0.03. Both types of models are found to be essentially stable to thermal perturbations. The mixing model reproduces the observed scalings of various cluster properties with temperature, and also explains the entropy floor seen in galaxy groups. 
Ramesh Narayan (1) and Woong-Tae Kim (1,2) ((1) Harvard-Smithsonian   CfA, (2) Seoul National University, Korea)