Astronomy and Astrophysics – Astrophysics
Scientific paper
2004-03-05
Astronomy and Astrophysics
Astrophysics
13 pages, Latex, 3 figures, 1 table, submitted to AJ
Scientific paper
10.1086/421003
Prompted by the discovery of the accreted Canis Major dwarf galaxy and its associated globular cluster (GC) system (Martin etal.), 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] > -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.
Brodie Jean
Forbes Duncan A.
Strader Jay
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