Evidence for a bottom-light initial mass function in massive star clusters

ABSTRACT We have determined stellar mass functions of 120 Milky Way globular clusters and massive Large Magellanic Cloud/Small Cloud star based on a comparison archival Hubble Space Telescope photometry with large grid direct N-body simulations. find strong correlation the global function slopes both their internal relaxation times lifetimes. Once dynamical effects are being accounted for, most compatible an initial described by broken power-law distribution N(m) ∼ mα break masses at 0.4 1.0 M⊙ αLow = −0.3 for stars m < M⊙, αHigh −2.30 > αMed −1.65 intermediate-mass stars. Alternatively, lognormal characteristic log MC −0.36 width σC 0.28 low-mass 1 also fit our data. do not significant environmental dependence cluster mass, density, velocity dispersion, or metallicity. Our results lead to larger fraction high-mass in compared canonical Kroupa/Chabrier functions, increasing efficiency self-enrichment helping alleviate budget problem multiple populations clusters. By comparing simulations, we finally that only simulations which black holes ejected natal birth kicks correctly reproduce observed correlations.