2018ApJ...863L..28M

The Gaia Sausage is an elongated structure in velocity space discovered by Belokurov et al. using the kinematics of metal-rich halo stars. They showed that it could be created by a massive dwarf galaxy (∼5 x 10¹⁰ M_☉) on a strongly radial orbit that merged with the Milky Way at a redshift z <= 3. This merger would also have brought in globular clusters (GCs). We seek evidence for the associated Sausage Globular Clusters (GCs) by analyzing the structure of 91 Milky Way GCs in action space using the Gaia Data Release 2 catalog, complemented with Hubble Space Telescope proper motions. There is a characteristic energy E_crit that separates the in situ objects, such as the bulge/disk clusters, from the accreted objects, such as the young halo clusters. There are 15 old halo GCs that have E > E_crit. Eight of the high-energy, old halo GCs are strongly clumped in azimuthal and vertical action, yet strung out like beads on a chain at extreme radial action. They are very radially anisotropic (β ∼ 0.95) and move on orbits that are all highly eccentric (e >= 0.80). They also form a track in the age-metallicity plane compatible with a dwarf galaxy origin. These properties are consistent with GCs associated with the merger event that gave rise to the Gaia Sausage.