Prompted by the discovery of the accreted Canis Major dwarf galaxy and its associated globular cluster ( GC ) system ( Martin et al . ) , we investigate the contribution of accreted GCs to the Galactic system .
The Canis Major GCs , and those associated with the Sagittarius dwarf galaxy , exhibit a range of galactocentric radii , prograde and retrograde motions , and horizontal branch morphologies , indicating that such properties are of limited use in identifying accreted GCs .
By contrast , we find that the age-metallicity relation ( AMR ) of these dwarf galaxies is distinct from that of the main Galactic GC distribution at intermediate-to-high metallicities ( [ Fe/H ] \gtrsim - 1.3 ) .
The accretion of GCs with a distinct AMR would explain much of the apparent age spread in the Galactic GC system .
The Canis Major and Sagittarius AMRs are similar to those of other Local Group dwarf galaxies and are consistent with a simple closed-box chemical enrichment model – a further indication that these GCs formed outside of the Milky Way .
The Canis Major GCs all have smaller-than-average sizes for their galactocentric distances , lending further support to their origin outside of the Milky Way .
Our findings suggest that accretion of similar mass dwarfs does not appear to have played a major role in building the stellar mass of the thick disk or bulge of the Milky Way .