Evolution of the mass function of the Galactic globular cluster system

Abstract

We investigate the evolution of the mass function of the Galactic globular cluster system (GCMF) taking into account the effects of stellar evolution, two-body relaxation, disk shocking and dynamical friction on the evolution of individual globular clusters.We have adopted a log-normal initial GCMF and we have studied in detail the dependence on the initial dispersion and mean value of the GCMF of the fraction of the initial number of clusters surviving after one Hubble time, of the final GCMF, and of the difference between the properties of the GCMF of clusters closer to the Galactic center and of those in the outer regions of the Galaxy.The initial log-normal shape of the GCMF is preserved in most cases and if a power-law in M is adopted for the initial GCMF, evolutionary processes tend to modify it into a log-normal GCMF. The difference between initial and final values of dispersion and mean value of the GCMF as well as the difference between the final values of these parameters for inner and outer clusters can be positive or negative depending on initial conditions.A significant effect of evolutionary processes does not necessarily give rise to a strong trend of the mean value of the GCMF with the galactocentric distance.The existence of a particular initial GCMF able to keep its initial shape and parameters unaltered during the entire evolution through a subtle balance between disruption of clusters and evolution of the masses of those which survive,suggested in Vesperini(1997),is confirmed. (abridged)