Young massive star clusters in M51

A search for young massive star clusters (YMCs) in the nearby face-on spira l galaxy M51 (NGC 5194) has been carried out using UBV CCD images from the prime focus camera on the Lick 3-m Shane telescope. The YMC population is f ound to be quite rich with a specific U-band luminosity T-L(U) similar to1. 4, consistent with the high current star formation rate (SFR) of this galax y. The brightest clusters have M-V similar to -12.5, far brighter than any young clusters currently known in the Milky Way and even surpassing the lum inosity of the R136 cluster in the 30 Dor complex in the Large Magellanic C loud. A few of the YMCs are examined on archive images from the Wide Field Planetary Camera (WF/PC2) on board the Hubble Space Telescope (HST), confir ming their cluster nature and providing estimates of their effective radii of 2-3 pc. The number of YMCs in M51 is compatible with extrapolation of a power-law luminosity function with exponent similar to -2 from a Milky Way- like population of open clusters. Both the SFR and T-L(U) of M51 are simila r to those of other cluster-rich spiral galaxies like NGC 1313 and M83.