Thursday, August 17, 2006

P. Kroupa: Cluster Formation and Dissolution

In last talk it was mentioned that 90% of all clusters in the Antennae get disrupted immediately and onlt the big ones will survive anyway, because it's only them who have a deep enouhg own potential well to retain the stars.

The speaker starts with cluster formation and talk about the simulations by Bonnell et al. which I just recently had included in my talk for a course back home. The efficiency in cluster formation is below 40%, which means that more than 60% of the gas in the cluster volume does not go into stars. When this gas is removed by radiation from the massive stars, the cluster suddenly loses this mass, becomes super-virial and therefore the cluster stars move quickly to larger radii. The cluster not only evaporates, it "pops".

The speaker argues that the "popping" of clusters might even account for the thick disk of galaxies, but I dont't really believe that, because, if I remember correctly, it is more likely that it is the infall of dwarf galaxies that build up the thick disk. It was just commented on this in the question session: the velocity dispersion of a smal thing is always smaller than that of the ISM itself.


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