Stellar orbital properties as diagnostics of the origin of the stellar halo

摘要

We examine metallicities, ages and orbital properties of halo stars in a Milky-Way like disk galaxy formed in the cosmological hydrodynamical MaGICC simulations. Halo stars were either accreted from satellites or they formed in situ in the disk or bulge of the galaxy and were then kicked up into the halo ("in situ/kicked-up" stars). Regardless of where they formed both types show surprisingly similar orbital properties: the majority of both types are on short-axis tubes with the same sense of rotation as the disk implying that a large fraction of satellites are accreted onto the halo with the same sense of angular momentum as the disk.