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Explaining the chemical trajectories of accreted and in-situ halo stars of the Milky Way

Brook, Chris B.; Kawata, Daisuke; Gibson, Brad K.; Gallart, Carme; Vicente, Andrés

Authors

Chris B. Brook

Daisuke Kawata

Carme Gallart

Andrés Vicente



Abstract

© 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. The Milky Way underwent its last significant merger ten billion years ago, when the Gaia-Enceladus-Sausage (GES) was accreted. Accreted GES stars and progenitor stars born prior to the merger make up the bulk of the inner halo. Even though these two main populations of halo stars have similar durations of star formation prior to their merger, they differ in [α/Fe]-[Fe/H] space, with the GES population bending to lower [α/Fe] at a relatively low value of [Fe/H]. We use cosmological simulations of a 'Milky Way' to argue that the different tracks of the halo stars through the [α/Fe]-[Fe/H] plane are due to a difference in their star formation history and efficiency, with the lower mass GES having its low and constant star formation regulated by feedback whilst the higher mass main progenitor has a higher star formation rate prior to the merger. The lower star formation efficiency of GES leads to lower gas pollution levels, pushing [α/Fe]-[Fe/H] tracks to the left. In addition, the increasing star formation rate maintains a higher relative contribution of Type II SNe to Type Ia SNe for the main progenitor population that formed during the same time period, thus maintaining a relatively high [α/Fe]. Thus the different positions of the downturns in the [α/Fe]-[Fe/H] plane for the GES stars are not reflective of different star formation durations, but instead reflect different star formation efficiencies.

Citation

Brook, C. B., Kawata, D., Gibson, B. K., Gallart, C., & Vicente, A. (2020). Explaining the chemical trajectories of accreted and in-situ halo stars of the Milky Way. Monthly notices of the Royal Astronomical Society, 495(3), 2645-2651. https://doi.org/10.1093/mnras/staa992

Journal Article Type Article
Acceptance Date Apr 7, 2020
Online Publication Date Apr 15, 2020
Publication Date 2020-07
Deposit Date Feb 1, 2021
Publicly Available Date Feb 2, 2021
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Oxford University Press
Peer Reviewed Peer Reviewed
Volume 495
Issue 3
Pages 2645-2651
DOI https://doi.org/10.1093/mnras/staa992
Keywords Galaxies: dwarf; Galaxies: evolution Galaxies: formation; Galaxies: haloes
Public URL https://hull-repository.worktribe.com/output/3681964
Publisher URL https://academic.oup.com/mnras/article-abstract/495/3/2645/5820236?redirectedFrom=fulltext

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Copyright Statement
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2020 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.







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