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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; Gómez, FA; ... Pakmor, R; + view all (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. 10.1093/mnras/staa2057. Green open access

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Abstract

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 [Math Processing Error] 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.

Type: Article
Title: The dual origin of the Galactic thick disc and halo from the gas-rich Gaia–Enceladus Sausage merger
Open access status: An open access version is available from UCL Discovery
DOI: 10.1093/mnras/staa2057
Publisher version: http://dx.doi.org/10.1093/mnras/staa2057
Language: Dutch
Additional information: This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: Galaxy: formation, Galaxy: kinematics and dynamics, Galaxy: structure, galaxies: spiral
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics
URI: https://discovery.ucl.ac.uk/id/eprint/10108072
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