The inner galaxy as a window on its early assembly: lessons from a cosmological Milky Way analogue
Abstract
Characterising the assembly history of the inner Milky Way is a key goal of upcoming spectroscopic surveys, yet disentangling its overlapping stellar components remains challenging. We investigate the chemodynamics of the centre of a Milky Way analogue in the Auriga Superstars cosmological hydrodynamical simulation suite, focusing on a high-resolution halo (~ 800 M_sun star particles) with a realistic galactic bar and accretion history. We classify stars within the inner 4 kpc into proto-galaxy, subsequent in-situ, and accreted components to assess their distinguishability using kinematics, dynamics, ages, and metallicities. Stellar net rotation declines sharply between [Fe/H]=0 and [Fe/H]=-1, marking the transition from disc-like in-situ stars to the proto-galaxy. While significant chemical and dynamical overlaps complicate the search for structures in energy-angular momentum (E-Lz) space, metal-poor stars ([Fe/H]<-1) at low energy form a remarkably pure (>97%) sample of proto-galaxy stars. Conversely, the high-energy, metal-poor tail offers the best chance of detecting accreted debris. However, at high energies the inner accreted halo is dominated by low-mass systems (M_star ~ 10^7 - 10^9 M _sun), not the earliest massive mergers. Dynamically, few clues remain from early mergers, and early enrichment is rapid and similar across progenitors. In-situ contamination is an issue for [Fe/H]>-1 throughout E-Lz space. Overall, while accurate stellar ages and high-precision chemical abundances may help further constrain the Milky Way's history, we should be cautious when associating stars with individual merger events in the inner galaxy.
Related
- Dark Energy Survey year 6 results: Cosmological constraints from galaxy clustering and weak lensing
- Tidal shells as clocks of galaxy mergers and tests of cosmological models
- Lens Modeling and Cosmological Inference from an Impure Sample of Galaxy-Galaxy Strong Lenses
- Lens Modeling and Cosmological Inference from an Impure Sample of Galaxy-Galaxy Strong Lenses
- Inductive Biases in Field-Level Cosmological Inference from Galaxy Catalogs
BibTeX
@misc{tomlinson2026inner,
title = {{The inner galaxy as a window on its early assembly: lessons from a cosmological Milky Way analogue}},
author = {Thomas Tomlinson and Francesca Fragkoudi and Andreia Carrillo and Alis Deason and Azadeh Fattahi and Rüdiger Pakmor and Robert J. J. Grand and Facundo A. Gómez and Freeke van de Voort and Rebekka Bieri},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.36164},
eprint = {2610.36164},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.36164},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - The inner galaxy as a window on its early assembly: lessons from a cosmological Milky Way analogue
AU - Thomas Tomlinson
AU - Francesca Fragkoudi
AU - Andreia Carrillo
AU - Alis Deason
AU - Azadeh Fattahi
AU - Rüdiger Pakmor
AU - Robert J. J. Grand
AU - Facundo A. Gómez
AU - Freeke van de Voort
AU - Rebekka Bieri
PY - 2026
DA - 2026/10/26
PB - arXiv
DO - 10.48550/arxiv.2610.36164
UR - https://arxiv.org/abs/2610.36164
AB - Characterising the assembly history of the inner Milky Way is a key goal of upcoming spectroscopic surveys, yet disentangling its overlapping stellar components remains challenging. We investigate the chemodynamics of the centre of a Milky Way analogue in the Auriga Superstars cosmological hydrodynamical simulation suite, focusing on a high-resolution halo (~ 800 M_sun star particles) with a realistic galactic bar and accretion history. We classify stars within the inner 4 kpc into proto-galaxy, subsequent in-situ, and accreted components to assess their distinguishability using kinematics, dynamics, ages, and metallicities. Stellar net rotation declines sharply between [Fe/H]=0 and [Fe/H]=-1, marking the transition from disc-like in-situ stars to the proto-galaxy. While significant chemical and dynamical overlaps complicate the search for structures in energy-angular momentum (E-Lz) space, metal-poor stars ([Fe/H]<-1) at low energy form a remarkably pure (>97%) sample of proto-galaxy stars. Conversely, the high-energy, metal-poor tail offers the best chance of detecting accreted debris. However, at high energies the inner accreted halo is dominated by low-mass systems (M_star ~ 10^7 - 10^9 M _sun), not the earliest massive mergers. Dynamically, few clues remain from early mergers, and early enrichment is rapid and similar across progenitors. In-situ contamination is an issue for [Fe/H]>-1 throughout E-Lz space. Overall, while accurate stellar ages and high-precision chemical abundances may help further constrain the Milky Way's history, we should be cautious when associating stars with individual merger events in the inner galaxy.
ER -