EDGE-INFERNO: The chemical signatures of assembly history in reionization fossils

Eric P. Andersson; Martin P. Rey; Alexander P. Ji; Justin I. Read; Oscar Agertz; Alexander H. Riley; Stacy Y. Kim; Astha Chaturvedi; Jennifer Mead; Kaley Brauer; Mordecai-Mark Mac Low; Andrew Pontzen

arXiv · 2610.18473

EDGE-INFERNO: The chemical signatures of assembly history in reionization fossils

Eric P. Andersson·Martin P. Rey·Alexander P. Ji·Justin I. Read·Oscar Agertz·Alexander H. Riley·Stacy Y. Kim·Astha Chaturvedi·Jennifer Mead·Kaley Brauer·Mordecai-Mark Mac Low·Andrew Pontzen

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Abstract

In galaxies, stellar populations represent a superposition of both in situ and accreted components, tracing internal chemical evolution as well as the histories of merged satellites. We investigate how assembly history shapes the chemical properties of present-day stellar populations in low-mass dwarf galaxies. We analyze a suite of EDGE-INFERNO star-by-star cosmological zoom-in simulations of galaxies with present-day halo mass $\sim1.4\times10^9\,{\rm M}_{\odot}$. We systematically vary galaxy growth while preserving the present-day halo mass, engineering our simulations to span a continuum of assembly histories. Early-forming systems form most of their stars in a single progenitor, with centrally concentrated star formation and a continuous enrichment history. In contrast, our late-forming systems assemble by accretion of multiple progenitors with their own stellar populations, resulting in fragmented star formation across several halos with independent chemical evolution tracks. These regimes produce qualitatively different chemical signatures: single-progenitor systems exhibit connected, well-defined trends in abundance space, while multi-progenitor systems show multiple, distinct stellar populations with limited overlap. We find that metallicity distribution functions provide initial constraints on assembly history for samples of at least $50$-$100$ member stars. Multi-element abundance analysis significantly improves the recovery of distinct components, although robust reconstruction still requires larger samples. Fully separating in situ and accreted populations likely requires kinematic information. Accreted stars can contribute substantially even at high metallicities in multi-progenitor systems, while external enrichment can cause accreted material to follow similar chemical trends as in situ stars, particularly in the single-progenitor regime.

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Eric P. Andersson, Martin P. Rey, Alexander P. Ji, Justin I. Read, Oscar Agertz, Alexander H. Riley, Stacy Y. Kim, Astha Chaturvedi, Jennifer Mead, Kaley Brauer, Mordecai-Mark Mac Low, Andrew Pontzen. 2026-10-13. EDGE-INFERNO: The chemical signatures of assembly history in reionization fossils. https://arxiv.org/abs/2610.18473

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