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Session 115 - Galaxies and Clusters of Galaxies.
Oral session, Thursday, January 16
We report the results of a recent numerical simulation of the merger of two galaxy clusters that includes the effects of radiative cooling. The objec tive of the simulation was to determine how a merger would affect a cluster cooling flow. Two clusters with a mass ratio of 4:1 were allowed to interact under the influence of their own gravity. Only the most massive cluster (10^15 M_\sun) had a significant cooling flow. The simulation was performed with a combined Hydrodynamics/N-body code on a grid with a resolution of 20 kpc. The N-body particles were evolved in 3-D while the gas evolution calculations were performed in 2-D since there is symmetry around the merger axis. We find two important results from this simulation. First, the cooling f low is completely disrupted some 0.25 Gyrs after core crossing. Second, there is no evi dence of a re-started cooling flow even 3 Gyrs after core crossing. This destruction o f the cooling flow is puzzling because recent surveys find that a large fraction of ga laxy clusters (60% to 90%) show evidence of cooling flows. Moreover, most clusters also show evidence of substructure which is believed to be a signature of a cluster i n the process of accreting mass or undergoing a merger. Thus, despite the eviden ce of recent mergers in cooling flow clusters, our result seems to suggest that massive mergers (i.e., mergers that can destroy cooling flows) are not common near the present epoch. We are in the process of exploring the effects of other galaxy cluster mergers (different mass ratios and relative gas contents) at higher resolution so that we can identify if less massive subcluste rs could also disrupt a cooling flow. This work was partially supported by NASA through grant NAGW-3152 and by the NSF through grant AST93-17596.
Program listing for Thursday