Comparing the temperatures of galaxy clusters from hydro-N-body   simulations to Chandra and XMM-Newton observations
  Theoretical studies of the physical processes in clusters of galaxies are mainly based on the results of numerical simulations, which in turn are often directly compared to X-ray observations. Although trivial in principle, these comparisons are not always simple. We show that the projected spectroscopic temperature of clusters obtained from X-ray observations is always lower than the emission-weighed temperature. This bias is related to the fact that the emission-weighted temperature does not reflect the actual spectral properties of the observed source. This has implications for the study of thermal structures in clusters, especially when strong temperature gradients, like shock fronts, are present. In real observations shock fronts appear much weaker than what is predicted by emission-weighted temperature maps.   We propose a new formula, the spectroscopic-like temperature function that better approximates the spectroscopic temperature, making simulations more directly comparable to observations 
P. Mazzotta (1,2), E. Rasia (3), L. Moscardini (4), G. Tormen (3) ((1)   Dip. di Fisica, Universita' di Roma "Tor Vergata" I...