Inverting the dynamical evolution of globular clusters: clues to their origin

TL;DR

This study investigates the dynamical evolution of globular clusters, revealing that two-body relaxation significantly influences their current properties and suggesting they may have formed differently from young massive clusters.

Contribution

The paper introduces a fast cluster evolution model to infer initial properties of Milky Way GCs, highlighting differences in initial mass functions compared to young clusters.

Findings

Two-body relaxation dominates the evolution of GCs with mass <10^6 Msun.

The initial mass function of GCs is flatter than that of young massive clusters.

G Cs likely formed differently from YMCs, influenced by stellar mass loss and relaxation processes.

Abstract

Scaling relations for globular clusters (GC) differ from scaling relations for pressure supported (elliptical) galaxies. We show that two-body relaxation is the dominant mechanism in shaping the bivariate dependence of density on mass and Galactocentric distance for Milky Way GCs with masses <10^6 Msun, and it is possible, but not required, that GCs formed with similar scaling relations as ultra-compact dwarf galaxies. We use a fast cluster evolution model to fit a parameterised model for the initial properties of Milky Way GCs to the observed present-day properties. The best-fit cluster initial mass function is substantially flatter (power-law index alpha =- 0.6+/-0.2) than what is observed for young massive clusters (YMCs) forming in the nearby Universe (alpha =~-2). A slightly steeper CIMF is allowed when considering the metal-rich GCs separately (alpha =~-1.2+/-0.4$). If stellar mass loss and two-body relaxation in the Milky Way tidal field are the dominant disruption mechanisms, then GCs formed differently from YMCs.