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S. S. Larsen (Copenhagen University Astronomical Observatory), T. Richtler (Sternwarte der Universitaet Bonn)
Using ground-based UBVRI CCD photometry, we have surveyed 21 nearby spiral galaxies in order to look for young massive star clusters (YMCs). We find that a large variety exists concerning the richness of the cluster systems, ranging from galaxies with practically no YMCs at all (e.g. NGC 300, NGC 45) to very rich cluster populations (NGC 1313, NGC 5236). The richness of the cluster systems as measured by the specific U-band luminosity of the clusters relative to that of their host galaxies (TU) does not appear to be correlated with the morphological type of the host galaxies, but we do find a correlation of TU with other properties of the host galaxies indicative of the star formation activity, such as the FIR luminosity and the optical surface brightness. These correlations also seem to hold when including literature data for starburst galaxies, indicating that the basic mechanism responsible for the formation of YMCs in ``normal'' galaxies and in starburst/merger galaxies may well be the same. We thus conclude that the formation of YMCs in starburst galaxies merely represents the ``tip of the iceberg'' of a much more general phenomenon that also takes place, although in a more quiescent mode, in a wide range of environments.
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