Pakmor, Rüdiger and Marinacci, Federico and Gómez, Facundo A. and Fragkoudi, Francesca and Fattahi, Azadeh and Deason, Alis J. and Belokurov, Vasily and Kawata, Daisuke and Grand, Robert J.J. (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.
We analyse a set of cosmological magneto-hydrodynamic 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% 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 onto 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.
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|Publisher Web site:||https://doi.org/10.1093/mnras/staa2057|
|Publisher 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.|
|Date accepted:||10 July 2020|
|Date deposited:||23 August 2020|
|Date of first online publication:||13 July 2020|
|Date first made open access:||23 August 2020|
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