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The biggest splash.

Grand, Robert J. J. and Evans, N. Wyn and Deason, Alis J. and Smith, Martin C. and Fattahi, Azadeh and Sanders, Jason L. and Belokurov, Vasily (2020) 'The biggest splash.', Monthly notices of the Royal Astronomical Society., 494 (3). pp. 3880-3898.


Using a large sample of bright nearby stars with accurate Gaia Data Release 2 astrometry and auxiliary spectroscopy we map out the properties of the principle Galactic components such as the “thin” and “thick” discs and the halo. We confirm previous claims that in the Solar neighborhood, there exists a large population of metal-rich ([Fe/H]>−0.7) stars on highly eccentric orbits. By studying the evolution of elemental abundances, kinematics and stellar ages in the plane of azimuthal velocity vφ and metallicity [Fe/H], we demonstrate that this metal-rich halo-like component, which we dub the Splash, is linked to the α-rich (or “thick”) disc. Splash stars have little to no angular momentum and many are on retrograde orbits. They are predominantly old, but not as old as the stars deposited into the Milky Way in the last major merger. We argue, in agreement with several recent studies, that the Splash stars may have been born in the Milky Way's proto-disc prior to the massive ancient accretion event which drastically altered their orbits. We can not, however, rule out other (alternative) formation channels. Taking advantage of the causal connection between the merger and the Splash, we put constraints of the epoch of the last massive accretion event to have finished 9.5 Gyr ago. The link between the local metal-rich and metal-poor retrograde stars is confirmed using a large suite of cutting-edge numerical simulations of the Milky Way's formation.

Item Type:Article
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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:26 March 2020
Date deposited:08 April 2020
Date of first online publication:07 April 2020
Date first made open access:08 April 2020

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