VINTERGATAN-GM : The cosmological imprints of early mergers on Milky-Way-mass galaxies

Summary, in English

We present a new suite of cosmological zoom-in hydrodynamical (≈ 20 pc spatial resolution) 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 ≈ 10¹² M_☉), 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 whose contribution to the GES can grow dynamically over time, and 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.

• Författare: Martin P. Rey; Oscar Agertz; Tjitske K. Starkenburg; Florent Renaud; Gandhali D. Joshi; Andrew Pontzen; Nicolas F. Martin; Diane K. Feuillet; Justin I. Read
• Avdelning/ar: Astrofysik; eSSENCE: The e-Science Collaboration
• Publiceringsår: 2023
• Språk: Engelska
• Sidor: 995-1012
• Publikation/Tidskrift/Serie: Monthly Notices of the Royal Astronomical Society
• Volym: 521
• Issue: 1
• Länkar: http://dx.doi.org/10.1093/mnras/stad513
• Dokumenttyp: Artikel i tidskrift
• Förlag: Oxford University Press
• Ämne: Astronomy, Astrophysics and Cosmology
• Nyckelord: galaxies: formation; galaxies: kinematics and dynamics; Galaxy: formation; Galaxy: halo; methods: numerical
• Status: Published
• ISBN/ISSN/Övrigt: ISSN: 0035-8711