The chemodynamics of prograde and retrograde Milky Way stars

Abstract

Context: The accretion history of the Milky Way is still unknown, despite the recent discovery of stellar systems that stand out in terms of their energy-angular momentum space, such as Gaia-Enceladus-Sausage. In particular, it is still unclear how these groups are linked and to what extent they are well-mixed. Aims: We investigate the similarities and differences in the properties between the prograde and retrograde (counter-rotating) stars and set those results in context by using the properties of Gaia-Enceladus-Sausage, Thamnos/Sequoia, and other suggested accreted populations. Methods: We used the stellar metallicities of the major large spectroscopic surveys (APOGEE, Gaia-ESO, GALAH, LAMOST, RAVE, SEGUE) in combination with astrometric and photometric data from Gaia's second data-release. We investigated the presence of radial and vertical metallicity gradients as well as the possible correlations between the azimuthal velocity, $v_{\varphi },$ and metallicity, [M/H], as qualitative indicators of the presence of mixed populations. Results: We find that a handful of super metal-rich stars exist on retrograde orbits at various distances from the Galactic center and the Galactic plane. We also find that the counter-rotating stars appear to be a well-mixed population, exhibiting radial and vertical metallicity gradients on the order of $\sim$ -0.04 dex/kpc and -0.06 dex/kpc, respectively, with little (if any) variation when different regions of the Galaxy are probed. The prograde stars show a $v_{\varphi }$-[M/H] relation that flattens -- and, perhaps, even reverses as a function of distance from the plane. Retrograde samples selected to roughly probe Thamnos and Gaia-Enceladus-Sausage appear to be different populations yet they also appear to be quite linked, as they follow the same trend in terms of the eccentricity versus metallicity space.

16 pages, accepted for publication in A&A

References in corpus (18)

• The Gaia mission
• Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties
• Two Stellar Components in the Halo of the Milky Way
• The Radial Velocity Experiment (RAVE): Fifth Data Release
• Evidence for Two Early Accretion Events That Built the Milky Way Stellar Halo
• Gaia Data Release 1: Catalogue validation
• Evidence from the H3 Survey that the Stellar Halo is Entirely Comprised of Substructure
• The Gaia-ESO Survey: the Galactic Thick to Thin Disc transition
• Star formation in a galactic outflow
• A First Constraint on the Thick Disk Scale Length: Differential Radial Abundances in K Giants at Galactocentric Radii 4, 8, and 12 kpc
• Distances and parallax bias in Gaia DR2
• Fashionably Late? Building up the Milky Way's Inner Halo
• The relationship between mono-abundance and mono-age stellar populations in the Milky Way disk
• A massive mess: When a large dwarf and a Milky Way-like galaxy merge
• Yule-Simpson's paradox in Galactic Archaeology
• Effects of the selection function on metallicity trends in spectroscopic surveys of the Milky Way
• The Rotation-Metallicity Relation for the Galactic Disk as Measured in the Gaia DR1 TGAS and APOGEE Data
• Cardinal kinematics: I. Rotation fields of the APOGEE Survey

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