Big Fish in Small Ponds: Massive Stars in the Low Mass Clusters of M83
  We have used multi-wavelength Hubble Space Telescope WFC3 data of the
starbursting spiral galaxy M83 in order to measure variations in the upper end
of the stellar initial mass function (uIMF) using the production rate of
ionizing photons in unresolved clusters with ages $\leq$ 8 Myr. As in earlier
papers on M51 and NGC 4214, the upper end of the stellar IMF in M83 is
consistent with an universal IMF, and stochastic sampling of the stellar
populations in the $\lessapprox$ 10$^{3}$ Msun clusters are responsible for any
deviations in this universality. The ensemble cluster population, as well as
individual clusters, also imply that the most massive star in a cluster does
not depend on the cluster mass. In fact, we have found that these small
clusters seem to have an over-abundance of ionizing photons when compared to an
expected universal or truncated IMF. This also suggests that the presence of
massive stars in these clusters does not affect the star formation in a
destructive way.
