The metal-rich halo tail extended in |z|: a characterization with Gaia DR2 and APOGEE

We report an analysis of the metal-rich tail ([Fe/H] > -0.75) of stars located at distances from the Galactic plane up to vertical bar z vertical bar similar to 10 kpc, observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE). We examine the chemistry, kinematics, and dynamics of this metal-rich sample using chemical abundances and radial velocities provided by the 14th APOGEE data release (DR14) and proper motions from the second Gaia data release (DR2). The analysis reveals three chemically different stellar populations in the [Mg/Fe] versus [Fe/H] space - a high-[Mg/Fe] and low-[Mg/Fe] populations, and a third group with intermediate [Mg/Fe] similar to +0.1 - as well as for other chemical elements. We find that they are also kinematically and dynamically distinct. The high-[Mg/Fe] population exhibits a prograde rotation which decreases down to 0 as vertical bar z(max)vertical bar increases, as well as eccentric orbits that are more bound and closer to the plane. The low-[Mg/Fe] stars are likely Sagittarius members, moving in less-bound orbits reaching larger distances from the centre and the Galactic plane. The intermediate-[Mg/Fe] stars resembles the two stellar overdensities lying about vertical bar z vertical bar similar to 5 kpc recently reported in the literature, for which a disc origin has been claimed. We report the identification of new members of these two disc-heated overdensities.