The formation history of the Milky Way disc with high-resolution
  cosmological simulations
  We analyse from an observational perspective the formation history and
kinematics of a Milky Way-like galaxy from a high-resolution zoom-in
cosmological simulation that we compare to those of our Galaxy as seen by Gaia
DR2 to better understand the origin and evolution of the Galactic thin and
thick discs. The cosmological simulation was carried out with the GADGET-3
TreePM+SPH code using the MUlti Phase Particle Integrator (MUPPI) model. We
disentangle the complex overlapping of stellar generations that rises from the
top-down and inside-out formation of the galactic disc. We investigate
cosmological signatures in the phase-space of mono-age populations and
highlight features stemming from past and recent dynamical perturbations. In
the simulation, we identify a satellite with a stellar mass of $1.2 \times
10^9$ M$_\odot$, i.e. stellar mass ratio $\Delta \sim 5.5$ per cent at the
time, accreted at $z \sim 1.6$, which resembles the major merger
Gaia-Sausage-Enceladus that produced the Galactic thick disc, i.e. $\Delta \sim
6$ per cent. We found at $z \sim 0.5-0.4$ two merging satellites with a stellar
mass of $8.8 \times 10^8$ M$_\odot$ and $5.1 \times 10^8$ M$_\odot$ that are
associated to a strong starburst in the Star Formation History, which appears
fairly similar to that recently found in the Solar Neighbourhood. Our findings
highlight that detailed studies of coeval stellar populations kinematics, which
are made available by current and future Gaia data releases and in synergy with
simulations, are fundamental to unravel the formation and evolution of the
Milky Way discs.
