This is the final version. Available from OUP via the DOI in this record
Recently acquired WFC3 UV (F275W and F336W) imaging mosaics under the Legacy Extragalactic UV Survey (LEGUS), combined with archival ACS data of M51, are used to study the young star cluster (YSC) population of this interacting system. Our newly extracted source catalogue contains 2834 cluster candidates, morphologically classified to be compact and uniform in colour, for which ages, masses and extinction are derived. In this first work we study the main properties of the YSC population of the whole galaxy, considering a mass-limited sample. Both luminosity and mass functions follow a power-law shape with slope -2, but at high luminosities and masses a dearth of sources is observed. The analysis of the mass function suggests that it is best fitted by a Schechter function with slope -2 and a truncation mass at 1.00 ± 0.12 × 105M⊙. Through Monte Carlo simulations, we confirm this result and link the shape of the luminosity function to the presence of a truncation in the mass function. A mass limited age function analysis, between 10 and 200 Myr, suggests that the cluster population is undergoing only moderate disruption. We observe little variation in the shape of the mass function at masses above 1 × 104M⊙over this age range. The fraction of star formation happening in the form of bound clusters in M51 is ~20 per cent in the age range 10-100 Myr and little variation is observed over the whole range from 1 to 200 Myr.
Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5–26555. These observations are associated with program # 13364. Support for program # 13364 was provided by NASA through a grant from the Space Telescope Science Institute. We acknowledge the help and suggestions provided by M. Gieles and N. Bastian. CLD acknowledges funding from the European Research Council for the FP7 ERC starting grant project LOCALSTAR. DAG kindly acknowledges financial support by the German Research Foundation (DFG) through program GO 1659/3-2. MF acknowledges support by the Science and Technology Facilities Council (grant number ST/P000541/1).