SIMBAD references

The relationship between the X-ray determined temperature T of the intracluster gas and the optical measured velocity dispersion σ of the cluster galaxies is often believed to be not only a straightforward but also robust test for the dynamical properties of galaxy clusters. Here, we present the σ-T relationship using the 94 clusters drawn from the largest sample of 149 clusters in literature, for which both σ and T are observationally determined. Employment of the doubly weighted orthogonal distance regression to our sample yields σ=10^2.47±0.06T^0.67±0.09, indicating an apparent deviation of dynamical state from that predicted by the isothermal and hydrostatic equilibrium model for galaxy clusters, though the average ratio β_spec of specific energy in galaxies to that in gas is found to be in excellent agreement with unity. It shows that a nonisothermal gas distribution with a mean polytropic index of γ=1.3 can account for the reported σ-T relationship, while overall clusters can still be regarded as dynamically-relaxed systems.