On the Origin of Mass Segregation in NGC 3603
  We present deep Hubble Space Telescope/Wide Field and Planetary Camera 2
photometry of the young HD 97950 star cluster in the giant H {\sc ii} region
NGC 3603. The data were obtained in 1997 and 2007 permitting us to derive
membership based on proper motions of the stars. Our data are consistent with
an age of 1 Myr for the HD 97950 cluster. A possible age spread, if present in
the cluster, appears to be small. The global slope of the
incompleteness-corrected mass function for member stars within 60$"$ is $\rm
\Gamma=-0.88\pm0.15$, which is flatter than the value of a Salpeter slope of
-1.35. The radially varying mass function shows pronounced mass segregation
ranging from slopes of $-0.26 \pm 0.32$ in the inner $5"$ to $-0.94\pm 0.36$ in
the outermost annulus ($40"$ -- $60"$). Stars more massive than 50 M$_{\odot}$
are found only in the cluster center. The $\Lambda$ minimum spanning tree
technique confirms significant mass segregation down to 30 M$_{\odot}$. The
dependence of $\Lambda$ on mass, i.e., that high-mass stars are more segregated
than low mass stars, and the (weak) dependence of the velocity dispersion on
stellar mass might imply that the mass segregation is dynamical in origin.
While primordial segregation cannot be excluded, the properties of the mass
segregation indicate that dynamical mass segregation may have been the dominant
process for segregation of high-mass stars.
