We carry out a joint spatial–kinematical–metallicity analysis of globular clusters ( GCs ) around the Andromeda Galaxy ( M31 ) , using a homogeneous , high-quality spectroscopic dataset .
In particular , we remove the contaminating young clusters that have plagued many previous analyses .
We find that the clusters can be divided into three major metallicity groups based on their radial distributions : ( 1 ) an inner metal-rich group ( [ Fe/H ] > -0.4 ) , ( 2 ) a group with intermediate metallicity ( with median [ Fe/H ] = -1 ) , ( 3 ) and a metal-poor group , with [ Fe/H ] < -1.5 .
The metal-rich group has kinematics and spatial properties like the disk of M31 , while the two more metal-poor groups show mild prograde rotation overall , with larger dispersions – in contrast to previous claims of stronger rotation .
The metal-poor GCs are the least concentrated group ; such clusters occur five times less frequently in the central bulge than do clusters of higher metallicity .
Despite some well-known differences between the M31 and Milky Way GC systems , our revised analysis points to remarkable similarities in their chemodynamical properties , which could help elucidate the different formation stages of galaxies and their GCs .
In particular , the M31 results motivate further exploration of a metal-rich GC formation mode in situ , within high-redshift , clumpy galactic disks .