Building Up the Globular Cluster System of the Milky Way: The Contribution of the Sagittarius Galaxy

Abstract

We demonstrate that there is a clear statistical correlation between the (X, Y, Z, V r ) phase-space distribution of the outer halo Galactic globular clusters (having 10 kpc ≤ R GC ≤ 40 kpc) and the orbital path of the Sagittarius dwarf spheroidal galaxy (Sgr dSph), as derived by Ibata & Lewis. At least four of the sample of 35 globular clusters in this distance range were formerly members of the Sagittarius galaxy (at the 95% confidence level) and are now distributed along the Sagittarius Stream, a giant tidal structure that surrounds the Milky Way. This is the first instance that a statistically significant structure associated with the Sgr dSph has been detected in the globular cluster population of the Galactic halo. Together with the four well-known globular clusters that are located near the center of this tidally disrupting dwarf galaxy, these clusters constitute ≳20% of the population of outer halo (R GC ≥ 10 kpc) clusters. The Sgr dSph was therefore not only an important contributor to the halo field-star population, but it also had a significant role in building up the globular cluster system of the Milky Way.