The MAGE Project: Size Evolution and Disk Formation in Massive Galaxies at Cosmic Dawn
Abstract
We investigate size evolution and disk formation with a new suite of eleven cosmological zoom-in simulations, Massive Assembly of Galaxies in the Early universe (MAGE), run with RAMSES at ∼10 pc resolution until z≃9. The target galaxies span stellar masses of M⋆≃2×108-3×1010 M⊙ at z=9. The stellar half-mass radius grows steeply with stellar mass at low masses, turns over near M⋆≃5×109 M⊙, and evolves weakly with redshift. The intrinsic UV sizes in MAGE overlap the compact end of observed distributions, including the compact strong-line systems, but not the more extended population at z>9. Dust, PSF-limited size measurements, and our overdense environments may contribute to this offset. In the simulations, stars dominate the mass within the half-mass radius above M⋆≃5×108 M⊙, where the central circular speed exceeds a characteristic stellar-feedback scale. Outflows are then increasingly retained within the galaxy, consistent with gas recycling on galactic rather than halo scales, which sustains central gas supply and drives a compaction-like central buildup. The turnover in size at M⋆≃5×109 M⊙ coincides with rapid growth of rotational support to v/σ≃1.5-$3$ in star-forming gas and stars younger than 10Myr, as the central circular speed exceeds the halo virial speed, which the star-forming gas velocity dispersion tracks. The subsequent low central gas fraction, declining central star formation, and younger outskirts suggest the onset of inside-out quenching.
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BibTeX
@misc{yao2026mage,
title = {{The MAGE Project: Size Evolution and Disk Formation in Massive Galaxies at Cosmic Dawn}},
author = {Zhiyuan Yao and Avishai Dekel and Romain Teyssier and Rachel Somerville and Nir Mandelker and Zachary Andalman and Ulrich Steinwandel and Zhaozhou Li},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.29070},
eprint = {2610.29070},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.29070},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - The MAGE Project: Size Evolution and Disk Formation in Massive Galaxies at Cosmic Dawn
AU - Zhiyuan Yao
AU - Avishai Dekel
AU - Romain Teyssier
AU - Rachel Somerville
AU - Nir Mandelker
AU - Zachary Andalman
AU - Ulrich Steinwandel
AU - Zhaozhou Li
PY - 2026
DA - 2026/10/28
PB - arXiv
DO - 10.48550/arxiv.2610.29070
UR - https://arxiv.org/abs/2610.29070
AB - We investigate size evolution and disk formation with a new suite of eleven cosmological zoom-in simulations, Massive Assembly of Galaxies in the Early universe (MAGE), run with RAMSES at ∼10 pc resolution until z≃9. The target galaxies span stellar masses of M_⋆≃2×10^8-3×10^10 M_⊙ at z=9. The stellar half-mass radius grows steeply with stellar mass at low masses, turns over near M_⋆≃5×10^9 M_⊙, and evolves weakly with redshift. The intrinsic UV sizes in MAGE overlap the compact end of observed distributions, including the compact strong-line systems, but not the more extended population at z>9. Dust, PSF-limited size measurements, and our overdense environments may contribute to this offset. In the simulations, stars dominate the mass within the half-mass radius above M_⋆≃5×10^8 M_⊙, where the central circular speed exceeds a characteristic stellar-feedback scale. Outflows are then increasingly retained within the galaxy, consistent with gas recycling on galactic rather than halo scales, which sustains central gas supply and drives a compaction-like central buildup. The turnover in size at M_⋆≃5×10^9 M_⊙ coincides with rapid growth of rotational support to v/σ≃1.5-$3$ in star-forming gas and stars younger than 10Myr, as the central circular speed exceeds the halo virial speed, which the star-forming gas velocity dispersion tracks. The subsequent low central gas fraction, declining central star formation, and younger outskirts suggest the onset of inside-out quenching.
ER -