ON THE ORIGIN OF MASS SEGREGATION IN NGC 3603

Abstract

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