Co-formation of the Galactic disc and the stellar halo

Understand

Using a large sample of Main Sequence stars with 7-D measurements supplied by Gaia and SDSS, we study the kinematic properties of the local (within ~10 kpc from the Sun) stellar halo.

• We demonstrate that the halo's velocity ellipsoid evolves strongly with metallicity.
• At the low [Fe/H] end, the orbital anisotropy (the amount of motion in the radial direction compared to the tangential one) is mildly radial with 0.2<beta<0.4.
• However, for stars with [Fe/H]>-1.7 we measure extreme values of beta~0.9.