On the Formation of Cool, Non-Flowing Cores in Galaxy Clusters via Hierarchical Mergers

Abstract

We present a new model for the creation of cool cores in rich galaxy clusters within a LambdaCDM cosmological framework using the results from high spatial dynamic range, adaptive mesh hydro/N-body simulations. It is proposed that cores of cool gas first form in subclusters and these subclusters merge to create rich clusters with cool, central X-Ray excesses. The rich cool clusters do not possess ``cooling flows'' due to the presence of bulk velocities in the intracluster medium in excess of 1000 km/sec produced by on-going accretion of gas from supercluster filaments. This new model has several attractive features including the presence of substantial core substructure within the cool cores, and it predicts the appearance of cool bullets, cool fronts, and cool filaments all of which have been recently observed with X-Ray satellites. This hierarchical formation model is also consistent with the observation that cool cores in Abell clusters occur preferentially in dense supercluster environments. On the other hand, our simulations overproduce cool cores in virtually all of our numerical clusters, the central densities are high, and physical core temperatures are often below 1 keV (in contrast to recent observations). We will discuss additional preliminary simulations to ``soften'' the cool cores involving star formation and supernova feedback.