EDGE-INFERNO: How chemical enrichment assumptions impact the individual stars of a simulated ultra-faint dwarf galaxy

¹ Department of Astrophysics, American Museum of Natural History 200 Central Park West New York NY 10024, USA
² Department of Physics, University of Bath Claverton Down Bath BA2 7AY, UK
³ Centre for Astrophysics Research, University of Hertfordshire Hatfield AL10 9AB, UK
⁴ University of Surrey, Physics Department, Guildford GU2 7XH, UK
⁵ Lund Observatory, Division of Astrophysics, Department of Physics, Lund University Box 43 SE-221 00 Lund, Sweden
⁶ Department of Astronomy & Astrophysics, University of Chicago, 5640 S Ellis Ave Chicago IL 60637, USA
⁷ Kavli Institute for Cosmological Physics, University of Chicago Chicago IL 60637, USA
⁸ NSF-Simons AI Institute for the Sky (SkAI), 172 E. Chestnut St. Chicago IL 60611, USA
⁹ Department of Astronomy, Columbia University, New York NY 10027, USA
¹⁰ Center for Astrophysics | Harvard & Smithsonian Cambridge MA 02138, USA

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Received: 7 November 2025
Accepted: 26 January 2026

Abstract

The chemical abundances of stars in galaxies are a fossil record of the star formation and stellar evolution processes that regulate galaxy formation, including the stellar initial mass function, the fraction and timing of type Ia supernovae (SNeIa), and nucleosynthesis inside massive stars. In this paper, we systematically explore uncertainties associated with modeling chemical enrichment in dwarf galaxies. We repeatedly simulate a single EDGE-INFERNO dwarf (M_★ ≈ 10⁵ M_⊙), varying the chemical yields of massive stars, the timing and yields of SNeIa, and the intrinsic stochasticity that arises from sampling individual stars and galaxy formation chaoticity. All simulations are high-resolution (3.6 pc), cosmological zoom-in hydrodynamical simulations that track the stellar evolution of all individual stars with masses of > 0.5 M_⊙. We find that SNeIa make significant contributions to the iron content of low-mass, reionization-limited galaxies, with possible variations in mean abundance ratios and [Fe/H] related to minor changes in their evolutionary timescales. In contrast, different massive star yields, accounting (or not) for stellar rotation, result in mean abundance variations comparable to those arising from stochasticity, with the possible exception of extremely rapidly rotating stars. Nonetheless, massive stars significantly affect the shape of abundance trends with [Fe/H], for example, through the existence (or not) of a bimodality in the [X/Fe]–[Fe/H] planes, particularly in [Al/Fe]. Finally, we find that the variance arising from random sampling severely limits the interpretation of single galaxies. Our analysis showcases the power of star-by-star cosmological models to unpick how both systematic uncertainties (e.g., assumptions in low-metallicity chemical enrichment) and statistical uncertainties (e.g., averaging over enough galaxies and stars within a galaxy) affect the interpretation of chemical observables in ultra-faint dwarf galaxies.