The impact of Population III stars on the elemental enrichment of ultra-faint galaxies in the FIRE-3 zoom-in simulations

Pratik J. Gandhi; Earl P. Bellinger; Marla Geha; Andrew Wetzel; Coral Wheeler; Yasmine J. Meziani; Jenna Samuel; Francisco J. Mercado; Jorge Moreno; Philip F. Hopkins

arXiv · 2611.05589

The impact of Population III stars on the elemental enrichment of ultra-faint galaxies in the FIRE-3 zoom-in simulations

Pratik J. Gandhi·Earl P. Bellinger·Marla Geha·Andrew Wetzel·Coral Wheeler·Yasmine J. Meziani·Jenna Samuel·Francisco J. Mercado·Jorge Moreno·Philip F. Hopkins

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Abstract

The observed stellar mass-metallicity relation for ultra-faint galaxies in the Local Group (LG) is in tension with many theoretical predictions, suggesting the need for modified or additional channels of elemental enrichment at low metallicities. We present a suite of FIRE-3 cosmological baryonic zoom-in simulations of isolated ultra-faint galaxies run to z=0 (maximum baryonic resolution ~ 30 Msun, 0.1 pc) and LMC-mass environments (maximum baryonic resolution ~ 110 Msun, 0.5 pc), with different sub-grid models for Population III stars. Under our Pop. III model(s), star particles forming below a critical metallicity Z_crit represent an initial mass function (IMF) consisting of only massive stars (8-100 Msun). We examine how various stellar feedback processes impact the star formation histories (SFHs) and elemental abundances of ultra-faint galaxies. We find that our Pop. III model variants introduce an effective metallicity floor in ultra-faints at z=0, at Z_floor ~ 1e-5 Zsun to 1e-3 Zsun or [Fe/H]_floor ~ -7 to -5 depending on the model. However, simply including the Pop. III model does not systematically guarantee that all (or even most) ultra-faints enrich up to [Fe/H] ~ -2.5 to fully resolve the tension with the observed mass-metallicity relation, even though we obtain some galaxies at that level. Crucially, the ultra-faints that do enrich in [Fe/H] to this level observed in the LG have extended SFHs after Pop. III enrichment and significant iron enrichment from white dwarf (Type Ia) supernovae, indicating that iron enrichment from Pop. III alone is not sufficient. We also examine the ways in which early-time Pop. III feedback impacts the metallicity distributions and [Mg/Fe] abundance ratios in ultra-faint galaxies, and make a prediction for the stellar mass - [Mg/H] metallicity relation from our simulations.

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Pratik J. Gandhi, Earl P. Bellinger, Marla Geha, Andrew Wetzel, Coral Wheeler, Yasmine J. Meziani, Jenna Samuel, Francisco J. Mercado, Jorge Moreno, Philip F. Hopkins. 2026-11-03. The impact of Population III stars on the elemental enrichment of ultra-faint galaxies in the FIRE-3 zoom-in simulations. https://arxiv.org/abs/2611.05589

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