Discovery of a Subsystem of Globular Clusters in M31: Possible Evidence for a Past Merging Event

We found a subsystem of globular clusters in M31 that appears to have a formation history separate from the rest. The member clusters of this subsystem, identified from their distinct distribution in the metallicity-distance diagram, (1) have a common medium metallicity range of -0.9<&sqbl0;Fe&solm0;H&sqbr0;<-0.4, (2) have a line-of-sight velocity distribution with no significant projected rotational motion, and (3) are populated outside the inner subsystem of globular clusters of similar metallicity that shows a significant net rotational motion as a whole. We suggest that this subsystem of globular clusters was formed during a merging event of a dwarf galaxy that took place well after the initial collapse event when most of the globular clusters in M31 were formed.