Homogeneous Metallicities and Radial Velocities for Galactic Globular Clusters

TL;DR

This study provides new radial velocities and metallicities for twenty Milky Way globular clusters, revealing significant revisions and internal abundance spreads, which are crucial for understanding the properties and evolution of these clusters.

Contribution

It offers the first spectroscopic measurements for poorly known clusters and confirms internal metallicity spreads in M54 and NGC 5824, advancing knowledge of globular cluster compositions.

Findings

Significant revisions of velocities and abundances for many clusters.

Confirmation of a sizable abundance spread in M54.

Evidence of internal metallicity spread in NGC 5824.

Abstract

Well determined radial velocities and abundances are essential for analyzing the properties of the Globular Cluster system of the Milky Way. However more than 50% of these clusters have no spectroscopic measure of their metallicity. In this context, this work provides new radial velocities and abundances for twenty Milky Way globular clusters which lack or have poorly known values for these quantities. The radial velocities and abundances are derived from spectra obtained at the Ca II triplet using the FORS2 imager and spectrograph at the VLT, calibrated with spectra of red giants in a number of clusters with well determined abundances. For about half of the clusters in our sample we present significant revisions of the existing velocities or abundances, or both. We also confirm the existence of a sizable abundance spread in the globular cluster M54, which lies at the center of the Sagittarius dwarf galaxy. In addition evidence is provided for the existence of a small intrinsic internal abundance spread (sigma [Fe/H](int) ~ 0.11-0.14 dex, similar to that of M54) in the luminous distant globular cluster NGC 5824. This cluster thus joins the small number of Galactic globular clusters known to possess internal metallicity ([Fe/H]) spreads.