Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 2610.29070

The MAGE Project: Size Evolution and Disk Formation in Massive Galaxies at Cosmic Dawn

Zhiyuan Yao·Avishai Dekel·Romain Teyssier·Rachel Somerville·Nir Mandelker·Zachary Andalman·Ulrich Steinwandel·Zhaozhou Li
View original source ↗Read source document ↗Export metadata ↓

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 $\sim10\,\mathrm{pc}$ resolution until $z\simeq9$. The target galaxies span stellar masses of $M_\star\simeq2\times10^8$-$3\times10^{10}\,M_\odot$ at $z=9$. The stellar half-mass radius grows steeply with stellar mass at low masses, turns over near $M_\star\simeq5\times10^9\,M_\odot$, 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 $M_\star\simeq5\times10^8\,M_\odot$, 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 $M_\star\simeq5\times10^9\,M_\odot$ coincides with rapid growth of rotational support to $v/σ\simeq1.5$-$3$ 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.

Explore related subjects

astro-ph.GA

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Zhiyuan Yao, Avishai Dekel, Romain Teyssier, Rachel Somerville, Nir Mandelker, Zachary Andalman, Ulrich Steinwandel, Zhaozhou Li. 2026-10-21. The MAGE Project: Size Evolution and Disk Formation in Massive Galaxies at Cosmic Dawn. https://arxiv.org/abs/2610.29070

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

ML in Astrophysical Turbulence I: Predicting Prestellar Cores in Magnetized Molecular Clouds using eXtreme Gradient Boosting

Giant Molecular Clouds (GMCs) are dominated by supersonic turbulence and magnetic fields, creating a complex network of shocks and filaments that regulate star formation, making it challenging to predict which individual gas parcels will collapse into star-forming cores. Here, we present an XGBoost machine learning framework to forecast the 3D Lagrangian trajectories and gravitational collapse fate of prestellar gas. Models were trained on $\sim 2.1$ million tracer particles from self-gravitating, turbulent magnetohydrodynamic (MHD) simulations. By mapping instantaneous point-wise states (position, velocity, density, and magnetic fields) to future coordinates, our regression model predicts continuous 3D spatial evolution over $0.25~t_{\rm ff}$ ($\approx 0.31\text{ Myr}$) with $R^2 > 0.99$. Concurrently, our classifier accurately ranks gravitational core susceptibility ($\text{AUC} = 0.975$). Using SHapley Additive exPlanations (SHAP), we interpret the model's decision hierarchy, revealing that local density, kinetic energy, and magnetic field magnitude dominate core identification. SHAP dependence analysis shows that the model re-derives a sharp non-linear collapse threshold at $\log_{10}ρ\approx 0.8$ above which magnetic fields amplify collapse predictions. The classification task reveals a conservative false-positive rate (37% precision) at absolute binary thresholds. We demonstrate that while point-wise ML models excel at kinematic advection, they mathematically lack the spatial context required to evaluate local differential operators (such as magnetic directional derivatives, thermal pressure gradients, or field curvature) that are physically necessary to stop collapse. This data-driven approach offers a computationally efficient foundation for advective subgrid modeling while highlighting the necessity of spatial architectures to establish absolute core-formation criteria.

astro-ph.GA↗
arXiv2026

The missing ultra-faint satellites of the Milky Way

We combine the highest resolution N-body simulation of a $\sim10^{12}M_\odot$ $Λ$CDM halo (Aquarius-A) with the semi-analytic model GALFORM to study the full satellite population of Milky Way (MW)-like galaxies. The model assumes that galaxies form only in subhalos whose peak circular velocity exceeds the hydrogen-cooling threshold, and predicts that the total number of satellites ever accreted into the main halo, down to arbitrarily low luminosity, should not exceed a few hundred. The model tracks satellites even after their halos become unresolved ("orphan" galaxies), and includes a novel treatment of dark matter and stellar tidal stripping which takes into account that $Λ$CDM subhalos survive tidal disruption because of their cuspy density profiles. Our results match the massive end of the observed MW satellite mass function and predict that many ultra-faint dwarfs (UFDs) with $M_V>-5$ are missing from the current MW satellite census. The missing UFDs are predicted to avoid the innermost regions of the host, and have properties overlapping those of the recently-discovered ultra-faint compact MW satellites (UFCSs). If the faintest dwarfs are initially as compact as UFCSs, our results suggest that many UFCSs should be dark matter-dominated dwarfs with velocity dispersions $1-3$ km/s which survived disruption because they inhabit the cusp of $Λ$CDM subhalos. UFCSs have predicted densities of $10^{10}$-$10^{11}\,M_\odot/$kpc$^3$, higher than those of more extended UFDs. If confirmed, our results provide strong support for the cuspy nature of $Λ$CDM halos and for the hydrogen-cooling threshold for galaxy formation.

astro-ph.GA↗
arXiv2026

Stardust Galaxies at z>9: A Dust-Origin Transition Behind the Excess of UV-Bright Galaxies

Recent JWST observations suggest that galaxies at z > 9 may be dominated by low-opacity SNe-produced dust before efficient ISM grain growth is established. This transition in dust origin and opacity could explain both the prevalence of galaxies with extremely low dust attenuation and the excess of UV-bright galaxies relative to most pre-JWST predictions. We investigate whether this transition, combined with evolving star-formation efficiency, can reproduce these observed properties. We develop a physically motivated attenuation framework combining (i) extinction laws for reverse-shock-processed SNe dust, (ii) metallicity- and dust-to-metal-dependent opacity scalings, and (iii) porous radiative-transfer geometries allowing partial UV-photon leakage. Unlike outflow-driven scenarios requiring large-scale gas evacuation, our approach preserves gas reservoirs while reducing effective UV opacity through dust composition and geometry. We introduce extinction-based, gas-based, and hybrid attenuation prescriptions linking SNe-dominated and ISM grain-growth dust regimes. We find that the observed A_FUV-M_star relation at z > 9 is best reproduced for an intrinsic FUV dust opacity kappa_UV(dust)=10^3 - 10^4 cm2/g, characteristic of low-opacity SNe dust, naturally producing very low attenuation even in gas-rich galaxies. This regime reproduces galaxies with extremely low dust attenuation (GELDAs), which dominate observed samples at z > 9. Applied to intrinsic UV luminosity function models, our SNe-dominated and hybrid prescriptions mainly suppress the brightest galaxies, bringing predictions into agreement with JWST measurements without requiring extreme star-formation efficiencies or dust-free interstellar media. Our results suggest that the UV-bright galaxy excess at z > 9 reflects a transition in dust origin and opacity during the earliest phases of galaxy evolution.

astro-ph.GA↗