RIGEL: Ultra-faint dwarf galaxy diversity shaped by inhomogeneous cosmic reionization
Abstract
Ultra-faint dwarf galaxies (UFDs) are among the smallest and oldest galaxies in the Universe and are widely regarded as relics of cosmic reionization. To investigate how reionization quenches star formation and shapes the diversity of UFDs, we present a suite of eight cosmological zoom-in simulations of isolated UFDs with present-day halo masses of ∼109 M⊙. The simulations are performed with the radiation-magnetohydrodynamic galaxy formation framework Realistic ISM modeling in Galaxy Evolution and Lifecycles (RIGEL), coupled to realistic large-scale radiation fields extracted from the THESAN reionization simulation. Despite residing in similar z=0 halos, the simulated galaxies span nearly two orders of magnitude in stellar mass and broadly reproduce the observed luminosities, sizes, metallicities, and stellar kinematics of Local Group UFDs. We find that reionization quenches star formation through a two-stage process. The arrival of the ionization front rapidly photoionizes the diffuse circumgalactic and intergalactic gas, suppressing further gas accretion onto the galaxy. Star formation nevertheless continues for several hundred Myr using the surviving self-shielded gas reservoir and ceases only after this gas is consumed or dispersed. Within 500 Myr after reionization, less than 40% of the initial gas mass remains in the halo, with photoevaporation constituting the dominant gas-loss channel. We further show that the halo mass at the time of reionization is a key parameter governing the subsequent evolution of UFDs. Galaxies residing in more massive halos at reionization retain gas for longer periods and undergo more extended chemical enrichment. Consequently, the halo mass at reionization strongly correlates with the final stellar mass, stellar age spread, and chemical evolution of the galaxy.
Related
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BibTeX
@misc{deng2026rigel,
title = {{RIGEL: Ultra-faint dwarf galaxy diversity shaped by inhomogeneous cosmic reionization}},
author = {Yunwei Deng and Hui Li and Ewald Puchwein and Boyuan Liu and Aaron Smith and Rahul Kannan and Federico Marinacci and Greg L. Bryan and Kung-Yi Su and Mark Vogelsberger},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.09267},
eprint = {2609.09267},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.09267},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - RIGEL: Ultra-faint dwarf galaxy diversity shaped by inhomogeneous cosmic reionization
AU - Yunwei Deng
AU - Hui Li
AU - Ewald Puchwein
AU - Boyuan Liu
AU - Aaron Smith
AU - Rahul Kannan
AU - Federico Marinacci
AU - Greg L. Bryan
AU - Kung-Yi Su
AU - Mark Vogelsberger
PY - 2026
DA - 2026/09/08
PB - arXiv
DO - 10.48550/arxiv.2609.09267
UR - https://arxiv.org/abs/2609.09267
AB - Ultra-faint dwarf galaxies (UFDs) are among the smallest and oldest galaxies in the Universe and are widely regarded as relics of cosmic reionization. To investigate how reionization quenches star formation and shapes the diversity of UFDs, we present a suite of eight cosmological zoom-in simulations of isolated UFDs with present-day halo masses of ∼10^9 M_⊙. The simulations are performed with the radiation-magnetohydrodynamic galaxy formation framework Realistic ISM modeling in Galaxy Evolution and Lifecycles (RIGEL), coupled to realistic large-scale radiation fields extracted from the THESAN reionization simulation. Despite residing in similar z=0 halos, the simulated galaxies span nearly two orders of magnitude in stellar mass and broadly reproduce the observed luminosities, sizes, metallicities, and stellar kinematics of Local Group UFDs. We find that reionization quenches star formation through a two-stage process. The arrival of the ionization front rapidly photoionizes the diffuse circumgalactic and intergalactic gas, suppressing further gas accretion onto the galaxy. Star formation nevertheless continues for several hundred Myr using the surviving self-shielded gas reservoir and ceases only after this gas is consumed or dispersed. Within 500 Myr after reionization, less than 40% of the initial gas mass remains in the halo, with photoevaporation constituting the dominant gas-loss channel. We further show that the halo mass at the time of reionization is a key parameter governing the subsequent evolution of UFDs. Galaxies residing in more massive halos at reionization retain gas for longer periods and undergo more extended chemical enrichment. Consequently, the halo mass at reionization strongly correlates with the final stellar mass, stellar age spread, and chemical evolution of the galaxy.
ER -