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 show 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 v _ { \phi } and metallicity [ Fe/H ] , we demonstrate that this metal-rich halo-like component , which we dub the Splash , is linked to the \alpha -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 .