The formation history of the Milky Way disc with high-resolution cosmological simulations

TL;DR

This study uses high-resolution cosmological simulations to analyze the formation and evolution of the Milky Way's disc, comparing results with Gaia data to understand the impact of mergers and perturbations on stellar populations.

Contribution

It provides a detailed simulation-based analysis of the Milky Way's disc formation, identifying merger events and their effects, and emphasizes the importance of Gaia data for understanding galactic evolution.

Findings

Identification of a satellite merger similar to Gaia-Sausage-Enceladus

Detection of recent mergers linked to starburst activity

Insights into the kinematic signatures of stellar populations

Abstract

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.