Chemo-dynamics of prograde and retrograde Milky Way stars. (arXiv:2009.07192v1 [astro-ph.GA])

Chemo-dynamics of prograde and retrograde Milky Way stars. (arXiv:2009.07192v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Kordopatis_G/0/1/0/all/0/1">Georges Kordopatis</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Recio_Blanco_A/0/1/0/all/0/1">Alejandra Recio-Blanco</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Schultheis_M/0/1/0/all/0/1">Mathias Schultheis</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hill_V/0/1/0/all/0/1">Vanessa Hill</a>

Context: The accretion history of the Milky Way is still unknown, despite the
recent discovery of stellar systems that stand out in energy-angular momentum
space, such as Gaia-Enceladus. 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 put those results in context with the
properties of Gaia-Enceladus, Thamnos and other suggested accreted populations.
Methods: We use the stellar metallicities of the major large spectroscopic
surveys (APOGEE, Gaia-ESO, GALAH, LAMOST, RAVE, SEGUE) in combination with
astrometric and photometric data coming from Gaia’s second data-release. We
investigate the presence of radial and vertical metallicity gradients as well
as the possible correlations between the azimuthal velocity $v_phi$ and
metallicity [M/H] as qualitative indicators of the presence of mixed
populations. Results: We find that (1) a handful of super metal-rich stars
exist on retrograde orbits at various distances from the Galactic center and
the Galactic plane. (2) The counter-rotating stars appear to be a well mixed
population, showing radial and vertical metallicity gradients of the order of
$sim -0.04$ dex/kpc and $-0.06$ dex/kpc, respectively, with little, if any,
variation when probing different regions of the Galaxy. (3) The prograde stars
show a $v_phi-[M/H]$ relation that flattens, and perhaps even reverses as a
function of distance from the plane. (5) Thamnos and Gaia-Enceladus stars seem
to be different populations yet very much linked, as they follow the same trend
in the eccentricity versus metallicity space.

Context: The accretion history of the Milky Way is still unknown, despite the
recent discovery of stellar systems that stand out in energy-angular momentum
space, such as Gaia-Enceladus. 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 put those results in context with the
properties of Gaia-Enceladus, Thamnos and other suggested accreted populations.
Methods: We use the stellar metallicities of the major large spectroscopic
surveys (APOGEE, Gaia-ESO, GALAH, LAMOST, RAVE, SEGUE) in combination with
astrometric and photometric data coming from Gaia’s second data-release. We
investigate the presence of radial and vertical metallicity gradients as well
as the possible correlations between the azimuthal velocity $v_phi$ and
metallicity [M/H] as qualitative indicators of the presence of mixed
populations. Results: We find that (1) a handful of super metal-rich stars
exist on retrograde orbits at various distances from the Galactic center and
the Galactic plane. (2) The counter-rotating stars appear to be a well mixed
population, showing radial and vertical metallicity gradients of the order of
$sim -0.04$ dex/kpc and $-0.06$ dex/kpc, respectively, with little, if any,
variation when probing different regions of the Galaxy. (3) The prograde stars
show a $v_phi-[M/H]$ relation that flattens, and perhaps even reverses as a
function of distance from the plane. (5) Thamnos and Gaia-Enceladus stars seem
to be different populations yet very much linked, as they follow the same trend
in the eccentricity versus metallicity space.

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