Table 1 is only availbale in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr ( 130.79.128.5 ) or via http : //cdsweb.u-strasbg.fr/Abstract.html The relationship between the X-ray determined temperature T of the intracluster gas and the optical measured velocity dispersion \sigma 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 \sigma - T relationship using the 94 clusters drawn from the largest sample of 149 clusters in literature , for which both \sigma and T are observationally determined .
Employment of the doubly weighted orthogonal distance regression to our sample yields \sigma = 10 ^ { 2.47 \pm 0.06 } T ^ { 0.67 \pm 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 \beta _ { 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 \gamma = 1.3 can account for the reported \sigma - T relationship , while overall clusters can still be regarded as dynamically-relaxed systems .