Star Cluster Survival in Star Cluster Complexes under Extreme Residual Gas Expulsion

After the stars of a new, embedded star cluster have formed they blow theremaining gas out of the cluster. Especially winds of massive stars anddefinitely the on-set of the first supernovae can remove the residual gas froma cluster. This leads to a very violent mass-loss and leaves the cluster out ofdynamical equilibrium. Standard models predict that within the cluster volumethe star formation efficiency (SFE) has to be about 33 per cent for sudden(within one crossing-time of the cluster) gas expulsion to retain some of thestars in a bound cluster. If the efficiency is lower the stars of the clusterdisperse mostly. Recent observations reveal that in strong star bursts starclusters do not form in isolation but in complexes containing dozens and up toseveral hundred star clusters, i.e. in super-clusters. By carrying outnumerical experiments for such objects placed at distances >= 10 kpc from thecentre of the galaxy we demonstrate that under these conditions (i.e. thedeeper potential of the star cluster complex and the merging process of thestar clusters within these super-clusters) the SFEs can be as low as 20 percent and still leave a gravitationally bound stellar population. Such an objectresembles the outer Milky Way globular clusters and the faint fuzzy starclusters recently discovered in NGC 1023.Comment: 21 pages, 8 figures, accepted by Ap