Galaxy archaeology - The quest for ancient mergers

Ackerl, C.; Leaman, R.; van de Ven, G.; Beasley, M.; Boecker, A.
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Austrian Early Career Conference 2024

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The hierarchical assembly of galaxies through mergers is a key channel of galaxy evolution in the ΛCDM cosmological model. Quantifying these ancient transformative accretion events from observations of present day galaxies is a crucial goal of extragalactic archeology. Achieving this goal is challenging as the dominant epoch of galaxy assembly lies in the early universe, and the stellar systems of the most significant mergers are well mixed by redshift ~0. However, stellar population properties and stellar dynamics derived from galaxy spectra encode information on the birth environment of accreted components. With modern observing techniques, it becomes feasible to access this information. In the Milky Way, astrometric and spectroscopic surveys like Gaia and GALAH have revealed chemodynamic tracers of the galaxy's assembly history in unprecedented detail. In external galaxies the picture is less clear. Despite advances in IFU observations and data analysis techniques, it remains challenging to recover and correctly interpret merger signatures from integrated light spectroscopy. In this talk I present a technique to overcome these limitations. We forward model the evolution of galaxies and their accreted subhalos in the baryonic and dark matter regime. The models produce two simultaneous predictions for observational signatures of a galaxy's assembly history, namely the stellar age-metallicity distribution in the galaxies, and their composite globular cluster populations. The resulting library of galaxy and star cluster population assembly histories will be publicly available in the future alongside with the model code. It is fully modular to allow the community to change prescriptions easily and grow the public library of galaxy assembly histories. This flexible approach to forward modelling galaxy archeological signatures of hierarchical assembly will complement simulation and data analysis efforts with the goal of achieving MW-like detail for recovered assembly histories of extragalactic systems.