The impact of metallicity-dependent mass-loss versus dynamical heating on the early evolution of star clusters

We have run direct N-body simulations to investigate the impact of stellar evolution and dynamics on the structural properties of young massive (~3×104M⊙) star clusters (SCs) with different metallicities (Z = 1, 0.1, 0.01 Z⊙). Metallicity drives the mass-loss by stellar winds and supernovae (SNe), with SCs losingmoremass at highmetallicity. We have simulated three sets of initial conditions, with different initial relaxation time-scale. We find that the evolution of the half-mass radius of SCs depends on how fast two-body relaxation is with respect to the lifetime of massive stars. If core collapse is slow in comparison with stellar evolution, then mass-loss by stellar winds and SNe is the dominant mechanism driving SC evolution, and metal-rich SCs expand more than metal-poor ones. In contrast, if core collapse occurs on a comparable time-scale with respect to the lifetime of massive stars, then SC evolution depends on the interplay between mass-loss and three-body encounters: dynamical heating by three-body encounters (mass-loss by stellar winds and SNe) is the dominant process driving the expansion of the core in metal-poor (metal-rich) SCs. As a consequence, the half-mass radius of metal-poor SCs expands more than that of metal-rich ones. We also find core radius oscillations, which grow in number and amplitude as metallicity decreases. © 2014 The Authors.