Relics of the Formation of the Galactic Halo from Gaia and APOGEE

Abstract

The solar neighborhood potentially contains a very large number of kinematic groups which are related to the various building blocks of the stellar halo. We explore the vicinity of the Milky Way through the use of high quality astrometric and spectroscopic data from the most recent releases by Gaia and APOGEE. We chemically select 663 halo stars and analyse their kinematics and orbital properties in order to investigate and characterise the possibly detectable signatures that remain in phase-space. We find evidence of statistically significant substructures among 177 stars, with velocity difference less than 20 km/s, that are classified in 15-25 kinematic groups and compared to the high velocity streamers by Re Fiorentin et al. 2015. The signal is even stronger among the stars with [Mg/Fe] < 0.2 dex, that more likely have been accreted; preliminary results are shown. The chemical properties of the kinematically selected moving groups are going to be analysed to reconstruct the accretion history of the stellar halo.