The global mass functions of 35 Galactic globular clusters: I. Observational data and correlations with cluster parameters

TL;DR

This study derives the global mass functions of 35 Galactic globular clusters, revealing their dependence on dynamical evolution and correlations with cluster parameters, suggesting most clusters are highly evolved.

Contribution

It provides the first comprehensive analysis of global mass functions for a large sample of clusters, linking their shapes to dynamical states and dark remnant retention.

Findings

Mass functions are well described by power-laws in certain mass ranges.

A strong anticorrelation exists between mass function slopes and relaxation times.

Massive remnant retention correlates with high mass-loss rates.

Abstract

We have derived the global mass functions of a sample of 35 Galactic globular clusters by comparing deep Hubble Space Telescope photometry with suitable multimass dynamical models. For a subset of 29 clusters with available radial velocity information we were also able to determine dynamical parameters, mass-to-light ratios and the mass fraction of dark remnants. The derived global mass functions are well described by single power-laws in the mass range $0.2 < m/M_\odot < 0.8$ with mass function slopes $\alpha>-1$. Less evolved clusters show deviations from a single-power law, indicating that the original shape of their mass distribution was not a power-law. We find a tight anticorrelation between the present-day mass function slopes and the half-mass relaxation times, which can be understood if clusters started from the same universal IMF and internal dynamical evolution is the main driver in shaping the present-day mass functions. Alternatively, IMF differences correlated with the present-day half-mass relaxation time are needed to explain the observed correlation. The large range of mass function slopes seen for our clusters implies that most globular clusters are dynamically highly evolved, a fact that seems difficult to reconcile with standard estimates for the dynamical evolution of clusters. The mass function slopes also correlate with the dark remnant fractions indicating a preferential retention of massive remnants in clusters subject to high mass-loss rates.