On the evolution of the Galactic globular cluster system

By means of a semi-analytical method, allowing us to follow the evolution of individual globular clusters spanning a large set of different initial conditions, we address the issue of the origin of some observational properties of the Galactic globular cluster system. After a preliminary study of some general properties of the main evolutionary processes by means of a discussion of the relevant time-scales and of a suitable ‘survival factor’, we investigate the evolution of systems of globular clusters located in a model of the Milky Way, starting from different initial conditions for the mass function of the system (power-law and log-normal) and for the distribution of concentrations of individual clusters. In particular, we study the role of the evolutionary processes in changing the spatial distribution and mass function of the cluster system, in establishing and/or preserving some of the observed correlations and trends between internal properties of globular clusters and between internal properties and location inside the host galaxy, and we provide an estimate for the rates of core collapse and the disruption of globular clusters. For the initial conditions considered in this paper, a significant fraction of clusters ( ~ 60 per cent) are lost because of disruption; the fraction of those undergoing core collapse is consistent with the present observational limits. The initial mass function and spatial distribution of the cluster system evolve quite significantly in one Hubble time and the evolution is toward a final state similar to the observed one. If the mass function is initially taken to be a log-normal distribution similar to the one currently observed in our Galaxy, its shape is not significantly altered during the entire simulation even though a significant number of clusters are disrupted before one Hubble time, which suggests that the present mass function might represent a sort of ‘quasi-equilibrium’ distribution.