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

TL;DR

This study investigates how different assumptions in chemical enrichment models affect the predicted stellar abundances in ultra-faint dwarf galaxies, highlighting the importance of detailed supernova modeling and the impact of stochastic sampling.

Contribution

It systematically explores the effects of varying chemical yields, supernova timing, and stochastic sampling on simulated stellar abundances in a high-resolution cosmological dwarf galaxy model.

Findings

Supernova Ia assumptions significantly influence mean abundance ratios.

Massive star yield variations affect abundance trend shapes, especially [Al/Fe].

Stochastic sampling limits the interpretability of single galaxy observations.

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 ($M_{\star} \approx 10^5 \, M_{\odot}$), 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 $>0.5\,{\rm M}_{\odot}$. We find that variations in SNIa assumptions make the largest difference in mean abundance ratios and [Fe/H], highlighting the importance of detailed SNIa modeling even in such low-mass reionization-limited galaxies. In contrast, different massive star yields, accounting (or not) for stellar rotation, result in mean abundances comparable to those arising from stochasticity. Nonetheless, they 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.