Cosmological implications of galaxy cluster evolution

We analyze with hydrodynamical simulations the evolution of galaxy clustersin a cosmological environment. Power ratios (Buote \& Tsai 1995) are used toquantitatively relate cluster morphologies to their dynamical states. Thesimulated clusters follow the same ``evolutionary track'' obeyed by a sample oflow-redshift $(z<0.2)$ ROSAT PSPC clusters (Buote \& Tsai 1996) indicating thatthe detailed evolution of individual simulated clusters is consistent withobserved clusters. However, the distribution of simulated clusters (for$\Omega=1$ standard Cold Dark Matter) along the evolutionary track at thepresent epoch, which indicates a measure of the present balance of clusterformation and relaxation rates, suggests that there are too many simulatedclusters with significant amounts of substructure to be consistent with theobservations, thus favoring a lower value of $\Omega$. Perpendicular to theevolutionary track the distributions of observed and simulated clusters areconsistent which may indicate a success of the cosmological model (e.g., powerspectrum). Analysis of high-redshift simulated clusters suggests that thedistribution of clusters both along and perpendicular to the evolutionary trackis effectively constant from $z\sim 0.6$ to the present but changessignificantly for $z > 0.6$.