Can cluster evaporation explain the missing thermal energy in galaxy clusters?

Resent observations of a number of galaxy clusters using the Sunyaev-Zel'dovich effect indicate that about of the baryonic mass is missing from the hot intracluster medium ( ICM), which is significantly larger than the 1/3 fraction of stars and cool gas, which account for only about 10%. Here we address the question of whether the remaining can be accounted for by the thermal evaporation of gas from clusters. We have found 22% +/- 10% that evaporation can occur only from the cluster surface,, and not from its interior. We evaluated particle r similar to r(vir) diffusion through the magnetized ICM for several scenarios of ISM turbulence and found that diffusivity is suppressed by at least a factor of 100 or more, compared to the Spitzer value. Thus, only particles at radii can evaporate. The diffusion of particles from inside the cluster, r less than or similar to 0.9r(vir) takes longer than the Hubble time. This lowers the cluster-averaged fraction of the evaporated hot gas to a few percent or less. However, if the missing hot component is indeed due to evaporation, this strongly constrains the magnetic field structure in the cluster envelope, namely, either the gas is completely unmagnetized (B <= 10(-21) G) in the cluster halo or the magnetic fields in the ICM are rather homogeneous and nonturbulent.