Evidence of a large scale positive rotation-metallicity correlation in the Galactic thick disk

Title: Evidence of a large scale positive rotation-metallicity correlation in the Galactic thick disk
Speaker: Alessandro Spagna (Osservatorio Astrofisico di Torino, Italy)
Time: 3 pm on 2018-11-08 (Thursday)
Location: Middle Conference Room, 3rd floor
   Although the existence of a thick disc in the Milky Way was revealed 35 years ago (Gilmore & Reid 1983) and its spatial, kinematic, and chemical properties are today better defined, its origin is still matter of debate.
   Proposed scenarios include the heating of a pre-existing thin disc through a minor merger, accretion of dwarf galaxies stars from disrupted satellites, or stars formed in situ from gas-rich mergers at high redshift. Such models predict characteristic trends on the kinematics and chemical abundances that can be used to discriminate the one, or the ones, favoured by the Milky Way.
   Recently, Re Fiorentin, Lattanzi & Spagna (2018) made up a new kinematic catalogue, containing positions, parallaxes and proper motions from Gaia DR2, plus radial velocities and chemical abundances derived with the APOGEE Stellar Spectra Parameter Pipeline
   We selected and classified 58 882 thin and thick disc tracers, with 5 < R < 13 kpc and within |z| < 3 kpc, for which full chemo-kinematical information is available. For the thin disc, we measured a negative circular velocity-metallicity correlation, in line with the expectations of the epicyclic stellar orbits convolved with the negative chemical radial gradient. Conversely, we found for the first time that the thick disc rotation-metallicity correlation is persistently positive within the 8 kpc range of Galactocentric distances investigated, in spite of its quasi-flat metallicity gradient.
   This result sets important constraints on recent theoretical studies on the formation and evolution of the Milky Way disc and on cosmological models of Galaxy formation.

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