Decoding the structure and formation history of the Milky Way halo with non-equilibrium orbit-based models

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The field of Galactic astronomy is flourishing thanks to enormous advances in observational facilities in recent years, however, the progress in the theoretical analysis and interpretation of the detailed observational picture is lagging behind.The outer parts of our Galaxy (the halo) are dominated by stars originating in other stellar systems engulfed by the Milky Way in the past, which retain important clues about the Galactic assembly history and properties of ancient accreted galaxies. These building blocks are usually identified by their coherent spatial, kinematic and chemical properties, but linking the populations of same-origin stars across the entire Galaxy is only possible with the knowledge of their orbits, which in turn depend on the gravitational potential. In turn, the orbital coherence of structures such as stellar streams is used to constrain the Galactic potential and hence the distribution of stars and dark matter, but current methods are usually restricted to stationary potentials. However, the ongoing encounter between our Galaxy and its largest satellite - the Large Magellanic Cloud - introduces significant temporal variations in the potential, disturbs the kinematics of halo stars and confounds the analysis.My project will provide solid theoretical foundation and analysis techniques for the current and upcoming large-scale surveys of the Milky Way system, and will shed light on its structure and formation history with the help of next-generation models. It will combine the techniques for finding localized structures with the underlying physical model for the evolving global gravitational field of the entire Galaxy, enabling for the first time to simultaneously identify and characterize the individual building blocks and constrain the time-dependent Galactic mass distribution. It will advance our understanding of the past and present of the Milky Way, and pave the road to a detailed exploration of other galaxies in the local Universe.