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The dual origin of the Galactic thick disc and halo from the gas-rich Gaia-Enceladus Sausage merger

Grand, RJJ, Kawata, D, Belokurov, V, Deason, AJ, Fattahi, A, Fragkoudi, F, Gomez, FA, Marinacci, F and Pakmor, R (2020) The dual origin of the Galactic thick disc and halo from the gas-rich Gaia-Enceladus Sausage merger. Monthly Notices of the Royal Astronomical Society, 497 (2). pp. 1603-1618. ISSN 0035-8711

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We analyse a set of cosmological magnetohydrodynamic simulations of the formation of Milky Way-mass galaxies identified to have a prominent radially anisotropic stellar halo component similar to the so-called 'Gaia Sausage' found in the Gaia data. We examine the effects of the progenitor of the Sausage (the Gaia-Enceladus Sausage, GES) on the formation of major galactic components analogous to the Galactic thick disc and inner stellar halo. We find that the GES merger is likely to have been gas-rich and contribute 10-50 per cent of gas to a merger-induced centrally concentrated starburst that results in the rapid formation of a compact, rotationally supported thick disc that occupies the typical chemical thick disc region of chemical abundance space. We find evidence that gas-rich mergers heated the proto-disc of the Galaxy, scattering stars on to less-circular orbits such that their rotation velocity and metallicity positively correlate, thus contributing an additional component that connects the Galactic thick disc to the inner stellar halo. We demonstrate that the level of kinematic heating of the proto-galaxy correlates with the kinematic state of the population before the merger, the progenitor mass, and orbital eccentricity of the merger. Furthermore, we show that the mass and time of the merger can be accurately inferred from local stars on counter-rotating orbits.

Item Type: Article
Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2020 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords: 0201 Astronomical and Space Sciences; Astronomy & Astrophysics
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press (OUP)
SWORD Depositor: A Symplectic
Date Deposited: 19 Apr 2023 12:06
Last Modified: 19 Apr 2023 12:06
DOI or ID number: 10.1093/mnras/staa2057
URI: https://researchonline.ljmu.ac.uk/id/eprint/19300
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