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 4 of the sample of 35 globular clusters in this distance range were formerly members of the Sgr galaxy (at the 95 % confidence level), and are now distributed along the Sgr 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 the building-up of the globular cluster system of the Milky Way.