Mortality and dust expulsion in early phases of stellar clusters.
  Evidence from NIR photometry of nearby, spiral galaxies
  It is often argued that young stellar clusters suffer a significant infant
mortality that is partly related to the expulsion of dust and gas in their
early phases caused by radiation pressure from hot stars and supernovae.
Near-infrared (J-K)-Mk diagrams of young stellar clusters in nearby spiral
galaxies show a bi-modal distribution that is consistent with a fast decline of
their intrinsic extinction at an early epoch.
  The distinct features in the color-magnitude diagrams (CMD) and the fast
change of colors for the youngest clusters allow us to place constraints on
their early evolutionary phases, including the time scale for the decreasing
extinction caused for instance by gas and dust expulsion.
  Monte Carlo simulations of cluster populations were performed using the
power-law distribution function g(M, t) ~ M^a t^gam. Integrated colors were
computed from Starburst99 models. The simulated near-infrared CMD were compared
with those observed for six grand-design, spiral galaxies using statistical
goodness-of-fit tests.
  The CMDs indicate a significant mortality of young, massive clusters with gam
= -1.4 +-0.5. High initial extinction Av = 8-11m and strong nebular emission
are required to reproduce the bi-modal color distributions of the clusters. An
extended star formation phase of longer than 5 Myr is suggested. The reduction
of the internal extinction of the clusters starts during their active star
formation and lasts for a period of 5-10 Myr.
