Constraining the structure and history of the Milky Way disk using Gaia

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Due to our proximity, the Milky Way provides a unique laboratory to study a massive disk galaxy in exquisite detail. We are currently living in the golden age of Galactic Archaeology, being able to investigate the formation history and structure of our Galaxy using multiple stellar populations with kinematics, chemical abundance, and age estimates with excellent precision. A paradigm shift has occurred in this field with the recent second and early third data releases (DR2 and EDR3) from ESA’s Gaia mission. Detailed diagnostics as never before have already been performed in the stellar multi-dimensional chemical abundance and kinematics phase space. This has fueled controversies about the dynamical state of the disk, the nature of spiral arms and central bar, and the effect of merging satellites (e.g., the Sagittarius dwarf galaxy). The goal of the proposal is to constrain key structural properties and the formation of the Milky Way disk, by using state-of-the-art numerical models for the interpretation of the Gaia DR3 data, combined with available and upcoming ground-based spectroscopic data (APOGEE, SDSS-V, GALAH and WEAVE, 4MOST), as well as the asteroseismic data from CoRoT, Kepler, and K2 missions. Chemical abundances and precise ages can be related to the birth positions of stars, which is extremely important for discriminating among competing models. Our models will be mostly based on the upcoming high-resolution HESTIA simulations at the AIP, which simulate the Milky Way in the Local Group environment using the state-of-the-art AREPO/Auriga galaxy formation code. In the comparison between models and data we will account for both selection effects and observational errors. We will provide tests for different Milky Way evolutionary scenarios by considering the following interconnected problems: (1) Understand the rich phase-space structure found in the Gaia DR2 data (ridges, arches, and snail-shell spiral in velocity-position space) in terms of recent perturbations from infalling galaxies and from internal agents (bar and spiral arms), (2) Recover the extended merger history of the Milky Way disk by studying disk thickness and velocity dispersion radial profiles for mono-age groups of stars, as well as changes in orbital properties with age, and (3) Constrain the Milky Way bar and spiral structure parameters by considering realistic time-evolving models in the cosmological context and combining dynamics, chemistry and age information.