Reconstructing the initial mass function of disc-bulge Galactic globular clusters from N-body simulations

TL;DR

This study develops a new evolutionary model calibrated with N-body simulations to reconstruct the initial mass function of Galactic globular clusters, revealing it was likely lognormal and formed in high-pressure regions of the early Galactic disc.

Contribution

The paper introduces a novel method to infer initial cluster masses from current data and demonstrates that a power-law initial mass function evolves into a lognormal distribution over time.

Findings

Initial mass function is well preserved as lognormal.

Power-law initial mass function evolves into lognormal within a Hubble time.

Globular clusters likely formed from giant molecular clouds in early high-pressure Galactic regions.

Abstract

We propose an evolutionary model to describe the dynamical evolution of star cluster systems in tidal fields, in which we calibrated the parametric equations defining the model by running direct N-body simulations of star clusters with a wide range of initial masses and set of orbital parameters, living within the external tidal field generated by a disc-like galaxy. We derived a new method to solve numerically the evolutionary equations, allowing us to infer constraints on the mass of a star cluster from its age, present-day mass, orbital parameters and external gravitational potential. The result has been applied to the metal-rich subsample of Galactic globular clusters, being a good representation of a disc-bulge population. We reconstructed the initial mass function of these objects from the present-day mass function, finding that a lognormal distribution is well preserved during the evolution of the globular cluster system. The evolution of a power-law initial mass function has been evaluated, confirming that it transforms into a lognormal distribution of the cluster masses within an Hubble time. Our results are consistent with a formation scenario in which metal-rich Galactic globular clusters formed from giant molecular clouds in high-pressure regions during the early phases of the evolution of the Galactic disc and bulge.