VINTERGATAN-GM: The cosmological imprints of early mergers on Milky-Way-mass galaxies
Résumé
We present a new suite of cosmological zoom-in hydrodynamical (≈20pc) simulations of Milky-Way mass galaxies to study how a varying mass ratio for a Gaia-Sausage-Enceladus (GSE) progenitor impacts the z=0 chemodynamics of halo stars. Using the genetic modification approach, we create five cosmological histories for a Milky-Way-mass dark matter halo (M200≈1012M⊙), incrementally increasing the stellar mass ratio of a z≈2 merger from 1:25 to 1:2, while fixing the galaxy's final dynamical, stellar mass and large-scale environment. We find markedly different morphologies at z=0 following this change in early history, with a growing merger resulting in increasingly compact and bulge-dominated galaxies. Despite this structural diversity, all galaxies show a radially-biased population of inner halo stars like the Milky-Way's GSE which, surprisingly, has a similar magnitude, age, [Fe/H] and [α/Fe] distribution whether the z≈2 merger is more minor or major. This arises because a smaller ex-situ population at z≈2 is compensated by a larger population formed in an earlier merger-driven starburst, with both populations strongly overlapping in the [Fe/H]−[α/Fe] plane. Our study demonstrates that multiple high-redshift histories can lead to similar z=0 chemodynamical features in the halo, highlighting the need for additional constraints to distinguish them, and the importance of considering the full spectrum of progenitors when interpreting z=0 data to reconstruct our Galaxy's past.
Domaines
Astrophysique [astro-ph]Origine | Fichiers éditeurs autorisés sur une archive ouverte |
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