On the dynamical state of galaxy clusters: insights from cosmological simulations - II.

Using a suite of cosmology simulations of a sample of >120 galaxy clusters with log (MDM, vir) 64 14.5. We compare clusters that form in purely dark matter (DM) run and their counterparts in hydro-runs and investigate four independent parameters that are normally used to classify dynamical state. We find that the virial ratio \u3b7 in hydro-dynamical runs is \u2dc10 per cent lower than in the DM run, and there is no clear separation between the relaxed and unrelaxed clusters for any parameter. Further, using the velocity dispersion deviation parameter \u3b6, which is defined as the ratio between cluster velocity dispersion \u3c3 and the theoretical prediction \u3c3 _t = 1a{G M_{total}/R}, we find that there is a linear correlation between the virial ratio \u3b7 and this \u3b6 parameter. We propose to use this \u3b6 parameter, which can be easily derived from observed galaxy clusters, as a substitute of the \u3b7 parameter to quantify the cluster dynamical state