Limits on thermal conduction in galaxy clusters

We have calculated lower limits for the global effective thermal conductivity in a sample of 165 Abell clusters. We assumed that cluster X-ray luminosity is compensated by a conductive heat flux which we then compare with an upper limit to the temperature gradient inferred from the cluster temperature and radius. This gives a lower limit to the thermal conductivity and therefore to the relative suppression from the Spitzer conductivity, kappa_{Sp}. Not a single cluster requires super-Spitzer values of thermal conduction to balance the observed X-ray luminosity. The suppression coefficient f=kappa/kappa_{Sp} is clustered in a range 10^{-2} < f < 0.4. A weak dependence of $f$ versus $z$ is observed over $0 < z <0.41$. Possible biases and/or selection effects are discussed.