The AGORA High-resolution Galaxy Simulations Comparison Project. X: Formation and Evolution of Galaxies at the High-redshift Frontier

TL;DR

The paper addresses the tension between JWST-detected luminous high-redshift galaxies and theoretical models by presenting the AGORA High-z Run, a cross-code comparison of six state-of-the-art hydrodynamical simulations using CosmoRun subgrid physics. It analyzes gas properties, stellar mass growth, metallicity, and mock JWST observables for halos with $M_{ m halo}$ around $10^{10}-10^{11}\,M_{ m\odot}$ at $z=10$, revealing good inter-code convergence for stellar mass but notable metallicity differences driven by feedback implementations. The results show that halos with $M_{ m halo}\ge 5\times 10^{10}\,M_{\odot}$ can reproduce JWST-like UV luminosities and metallicities at $10\le z\le 12$ without extra high-$z$ subgrid physics, though properties tend to fall short at $z\sim 13-14$; dust attenuation is a major factor shaping UV brightness. The study highlights the importance of feedback modeling and dust in shaping early galaxy observables and sets the stage for higher-resolution, more physics-rich simulations, which will further illuminate Cosmic Dawn galaxy formation.

Abstract

Recent observations from JWST have revealed unexpectedly luminous galaxies, exhibiting stellar masses and luminosities significantly higher than predicted by theoretical models at Cosmic Dawn. In this study, we present a suite of cosmological zoom-in simulations targeting high-redshift ($z \geq 10$) galaxies with dark matter halo masses in the range $10^{10} - 10^{11}\ {\rm M}_{\odot}$ at $z=10$, using state-of-the-art galaxy formation simulation codes (Enzo, Ramses, Changa, Gadget-3, Gadget-4, and Gizmo). This study aims to evaluate the convergence of the participating codes and their reproducibility of high-redshift galaxies with the galaxy formation model calibrated at relatively low redshift, without additional physics for high-redshift environments. The subgrid physics follows the AGORA CosmoRun framework, with adjustments to resolution and initial conditions to emulate similar physical environments in the early universe. The participating codes show consistent results for key galaxy properties (e.g., stellar mass), but also reveal notable differences (e.g., metallicity), indicating that galaxy properties at high redshifts are highly sensitive to the feedback implementation of the simulation. Massive halos (${\rm M}_{\rm halo}\geq5\times10^{10}\,{\rm M}_{\odot}$ at $z=10$) succeed in reproducing observed stellar masses, metallicities, and UV luminosities at $10\leq z\leq12$ without requiring additional subgrid physics, but tend to underpredict those properties at higher redshift. We also find that varying the dust-to-metal ratio modestly affects UV luminosity of simulated galaxies, whereas the absence of dust significantly enhances it. In future work, higher-resolution simulations will be conducted to better understand the formation and evolution of galaxies at Cosmic Dawn.

Figures (16)

• Figure 1: The dark matter surface densities at $z=10$ for five massive halos across six different hydrodynamical simulations, "High-z Run". The projections are taken through a 40 kpc slice and the target halo's virial radius $R_{\rm vir}$ identified by the ROCKSTAR halo finder 2013ApJ...762..109B is denoted with a white circle. The simulations are conducted by Santi Roca-Fàbrega (Ramses), Hyeonyong Kim (Enzo, Gadget-3, Gizmo), Héctor Velázquez (Changa), and Pablo Cuadrado (Gadget-4). See Section \ref{['sec:simulation']} for detailed information including subgrid physics, initial condition, and refinement schemes of these simulations.
• Figure 2: Gas density projections at $z=10$ from the High-z Run for the five target halos. The virial radius of each target halo is indicated by a white dashed circle. While the participating codes show good overall agreement in gas distribution, some inter-code differences in the gas concentration in the circumgalactic region are notable. See Section \ref{['sec:gas_properties']} for more information.
• Figure 3: Density-weighted projections of gas temperature at $z=10$ from the High-z Run for the five target halos. Similar to Figure \ref{['fig:density_projection']}, white circles indicate the virial radius of the halo. As discussed in Paper VI, the adaptive mesh refinement (AMR) codes Enzo and Ramses exhibit stronger contrast between the cold, high-density clouds and the hot, low-density bulk when compared to the smoothed particle hydrodynamics (SPH) codes in the circumgalactic medium (CGM). See Section \ref{['sec:gas_properties']} for more information.
• Figure 4: Two-dimensional probability distribution functions (PDFs) of gas density and temperature at $z=10$ in the High-z Run. Gas within the $R_{\rm vir}$ of the halos is included, with the color representing the total gas mass in each bin. Star formation density threshold ($n_{\rm H} = 1 \,\rm cm^{-3}$) and feedback-free starbursts (FFB) density threshold ($n_{\rm H} = 3000 \,\rm cm^{-3}$) are annotated as vertical black and red dashed lines, respectively. Halos with virial masses above the FFB mass threshold ($\rm M_{\rm halo, z=10} = 3.5 \times 10^{10}\,{\rm M}_{\odot}$; Halos 3, 4, and 5) contain denser gas than halos below the threshold. Ramses consistently produces very dense gas regardless of halo mass, in contrast to other codes. See Section \ref{['sec:gas_properties']} for more information.
• Figure 5: Evolution of stellar mass histories in the High-z Run. Each panel shows the results for a different target halo. Stellar mass is calculated as the total stellar mass within $R_{\rm vir}$ of the halo, following the methodology adopted for Figure 4 in Paper IV. To compare with observations, in the bottom right panel we present the mean value (thick red line) and the minimum–maximum range (gray shaded region) of Halo 5 and JWST observation data (black dots with error bars) from the following works: 2023AA...677A..88B2023ApJ...952...74T2023ApJ...957L..34W2024ApJ...960...56H2024ApJ...973....8H2024ApJ...970...31R2025AA...696A..87C2025ApJ...992..212W. The observation data points are replicated in other panels as translucent gray dots. Despite some variations in stellar mass across simulations, the High-z Run Halo 5 results show good agreement with observations, reproducing similar stellar masses except at $z \sim 14$. See Section \ref{['sec:stellar']} for more information.