Dynamical evolution of stars and star clusters in the inner Galactic bulge

The inner few hundred parsecs of the Galactic bulge contain stars of essentially all possible ages. Recent massive star formation there is evidenced by the observations of three clusters containing luminous emission-line stars: one in the central parsec and two others located a few tens of parsecs away from the center: the Arches and Quintuplet clusters. The latter two clusters are very young and compact, making them interesting in terms of their dynamical evolution. For the first part of this study, we have investigated the dynamical evolution of these clusters using anisotropic Fokker-Planck models and real-number N-body simulations. The short relaxation times attributable to the clusters' compactness and strong tidal fields there are found to cause the clusters with a mass ≲2x104M⊙ to evaporate in only ≲ 10 Myr. The comparison of N-body simulations and HST/ NICMOS observations of the Arches cluster suggests a total initial mass of 2x104M⊙ and an initial mass function slope of alpha = 1.75 (the Salpeter function has 2.35). The lower stellar mass limit, the presence of primordial binaries, the amount of initial mass segregation, and the choice of initial density profile (King or Plummer models) are found to not significantly affect the dynamical evolution of these clusters. The second part of this study involves the dynamical evolution of isolated stars or stars resulting from cluster dissolution. Monte Carlo simulations of the scatterings in the presence of the non-axisymmetric gravitational potential are performed, based on the hypothesis that stars formed in a flat molecular layer in the inner bulge are scattered by giant molecular clouds. The simulation results agree well with the observed stellar density profiles and the observed aspect ratio of the stellar distribution, leading to the conclusion that scattering by giant molecular clouds is likely to be the predominant mechanism for the vertical diffusion of stars in the inner Galactic bulge.