Measuring Consistent Masses for 25 Milky Way Globular Clusters

TL;DR

This study measures the dynamical properties of 25 Milky Way globular clusters, including velocity dispersions and masses, and analyzes trends with metallicity and mass using a large, uniform dataset.

Contribution

It provides a comprehensive, uniform set of dynamical parameters for 25 clusters, including new velocity dispersion measurements and analysis of mass-to-light ratios and rotation.

Findings

Mass-to-light ratio increases with cluster mass.

Metal-rich clusters have lower than expected M/L ratios.

No clear trend of rotation with metallicity.

Abstract

We present central velocity dispersions, masses, mass to light ratios ($M/L$s), and rotation strengths for 25 Galactic globular clusters. We derive radial velocities of 1951 stars in 12 globular clusters from single order spectra taken with Hectochelle on the MMT telescope. To this sample we add an analysis of available archival data of individual stars. For the full set of data we fit King models to derive consistent dynamical parameters for the clusters. We find good agreement between single mass King models and the observed radial dispersion profiles. The large, uniform sample of dynamical masses we derive enables us to examine trends of $M/L$ with cluster mass and metallicity. The overall values of $M/L$ and the trends with mass and metallicity are consistent with existing measurements from a large sample of M31 clusters. This includes a clear trend of increasing $M/L$ with cluster mass, and lower than expected $M/L$s for the metal-rich clusters. We find no clear trend of increasing rotation with increasing cluster metallicity suggested in previous work.