Origin of the Excess of High-energy Retrograde Stars in the Galactic Halo

We report on the very low -element abundances of a group of metal-poor stars with high orbital energy and with large retrograde motion in the Milky Way halo, whose excess has been reported recently from metallicity and kinematics. We constructed a sample of halo stars with measured abundances and pr...

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Bibliographic Details
Published in:Astrophysical journal. Letters 2019-04, Vol.874 (2), p.L35
Main Authors: Matsuno, Tadafumi, Aoki, Wako, Suda, Takuma
Format: Article
Language:English
Subjects:
Abundance
Angular momentum
Archaeology
Dwarf galaxies
Enceladus
Energy
Galactic halos
Galaxy: abundances
Galaxy: halo
Galaxy: kinematics and dynamics
Galaxy: stellar content
Galaxy: structure
High energy astronomy
Iron
Kinematics
Metallicity
Milky Way
Organic chemistry
Populations
Star & galaxy formation
Star formation
Stars
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Summary:We report on the very low -element abundances of a group of metal-poor stars with high orbital energy and with large retrograde motion in the Milky Way halo, whose excess has been reported recently from metallicity and kinematics. We constructed a sample of halo stars with measured abundances and precise kinematics, including ∼880 stars with [Fe/H] < −0.7, by crossmatching the Stellar Abundances for Galactic Archaeology database to the second data release of Gaia. Three regions in the energy-angular momentum space have been selected: the innermost halo, Gaia Enceladus/Sausage, and the high-energy retrograde halo. While the innermost halo and Gaia Enceladus regions have chemical abundances consistent with high- and low- populations in the halo, respectively, chemical abundances of stars in the high-energy retrograde halo are different from the two populations; their [X/Fe], where X represents Na, Mg, and Ca, are even lower than those in Gaia Enceladus. These abundances, as well as their low mean metallicity, provide a new support for the idea that the retrograde component is dominated by an accreted dwarf galaxy which has a longer star formation timescale and is less massive than Gaia Enceladus/Sausage.
ISSN:2041-8205
2041-8213
DOI:10.3847/2041-8213/ab0ec0