An updated survey of globular clusters in M 31. III. A spectroscopic metallicity scale for the Revised Bologna Catalog

TL;DR

This paper provides a new homogeneous spectroscopic metallicity scale for 245 old globular clusters in M31, revealing a likely non-unimodal metallicity distribution and a strong correlation between metallicity and kinematics.

Contribution

It introduces a new metallicity estimation method for M31 globular clusters and compares their distribution and kinematic properties with those of the Milky Way.

Findings

Metallicity distribution likely not unimodal.

Confirmed correlation between metallicity and kinematics.

Metal-rich clusters are centrally concentrated and share galactic rotation.

Abstract

We present a new homogeneous set of metallicity estimates based on Lick indices for 245 old globular clusters of the M31 galaxy comprised in the Revised Bologna Catalog. The metallicity distribution of the M31 globular clusters is briefly discussed and compared with that of the Milky Way. Simple parametric statistics suggests that the [Fe/H] distribution is likely not unimodal. The strong correlation between metallicity and kinematics found in previous studies is confirmed. The most metal-rich GCs tend to be packed at the center of the system and share the galactic rotation as traced by the HI disk. Although the velocity dispersion around the curve increases with decreasing metallicity, also clusters with [Fe/H]<-1.0 display a clear rotational pattern, at odds with their Milky Way counterparts.