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Abstract: We estimate the dynamical masses of several young ~10 Myr massive starclusters in two interacting galaxies, NGC 4038-4039 -The Antennae- and NGC1487, under the assumption of virial equilibrium. These are compared withphotometric mass estimates from K-band photometry and assuming a standardKroupa IMF. The clusters were selected to have near-infrared colors dominatedby red supergiants, and hence to be old enough to have survived the earliestphases of cluster evolution when the interstellar medium is rapidly swept outfrom the cluster, supported by the fact that there is no obvious Halphaemission associated with the clusters. All but one of the Antennae clustershave dynamical and photometric mass estimates which are within a factor ~2 ofone another, implying both that standard IMFs provide a good approximation tothe IMF of these clusters, and that there is no significant extra-virialmotion, as would be expected if they were rapidly dispersing. These resultssuggest that almost all of the Antennae clusters in our sample have survivedthe gas removal phase as bound or marginally bound objects. Two of the threeNGC 1487 clusters studied here have M dyn estimates which are significantlylarger than the photometric mass estimates. At least one of these two clusters,and one in the Antennae, may be actively in the process of dissolving. Theprocess of dissolution contributes a component of non-virial motion to theintegrated velocity measurements, resulting in an estimated M dyn which is toohigh relative to the amount of measured stellar light. The dissolutioncandidates in both galaxies are amongst the clusters with the lowestpressures-densities measured in our sample.

Autor: Sabine Mengel, Matthew D. Lehnert, Niranjan A. Thatte, William D. Vacca, Brad Whitmore, Rupali Chandar


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