Cosmological Simulation with Population III Stellar Feedback and Metal Enrichment I: Model Description And Convergence Test

TL;DR

The study presents a new Pop III + Pop II subgrid framework implemented in AREPO to quantify how the first stars regulate early galaxy formation through IMF-weighted SN feedback, non-equilibrium chemistry, metal cooling, and approximate LW/ionizing radiation transport. By running $1\,{\rm cMpc}/h$ cosmological boxes from $z=127$ to $z=10$, the authors demonstrate that the model reproduces UV-inferred Pop II SFRD and yields a metal-enriched volume filling factor of about $1\%$ by $z=10$; convergence is achieved once halos with $M_{\rm subhalo}\gtrsim10^{6.5}\,M_{\odot}$ are resolved, with total stellar mass by $z=10$ largely insensitive to initial conditions or resolution. The framework uses a stochastic IMF sampling for SN feedback, a diffusion-based turbulent metal mixing model, and a two-band radiation scheme to capture essential feedback while maintaining computational tractability (roughly $10^4$ CPU hours per fiducial run). Together, these results establish a robust, efficient platform for future parameter studies of Pop III IMF variations, X-ray feedback, and environmental effects on early galaxy formation in cosmological volumes.

Abstract

We present a new Pop III + Pop II subgrid framework implemented in the moving-mesh code {\sc arepo}, designed to study the impact of Pop III feedback on star formation in the early universe. The framework combines primordial non-equilibrium chemistry, metal-line cooling, IMF-sampled stellar evolution with SN feedback, and approximate Lyman-Werner (LW) and ionizing radiation transport. We run a suite of $1c{\rm Mpc}/h$ box simulations with different initial conditions and resolutions from $z=127$ to $z=10$. The highest gas mass and spatial resolution in the fiducial simulation reach $\sim10\,{\rm M_{\odot}}$ and $\sim4\,{\rm pc}$, respectively. The model successfully reproduces the UV-inferred Pop II star formation rate density (SFRD) from recent JWST observations across all initial conditions, with only minor variation driven by local halo interactions and LW irradiation. We find that the volume filling factor of metal-enriched gas converges to $\sim1\%$ at $z=10$. Convergence is achieved once subhalos with $M_{\rm subhalo}\gtrsim 10^{6.5}\,{\rm M_{\odot}}$ are resolved, and the total stellar mass at $z=10$ is largely insensitive to initial conditions or the resolution considered in this work. A fiducial simulation requires $\sim 10^4$ CPU hours, making the framework computationally tractable for larger box simulations and enabling future large parameter studies of stellar physics or environment effects such as Pop III IMF variations, X-ray radiation, or the streaming velocity at high redshift.

Figures (12)

• Figure 1: The gas surface density, mass-weighted temperature, and metallicity distribution in the simulations with different initial conditions from $z=20$ to $z=10$. From the top to the bottom is IC0 (upper), IC1 (middle), and IC2 (bottom). The blue points represent the Pop III star while the black points represent the Pop II star. The first Pop III star forms at $z=20-18$ in these three simulations.
• Figure 2: Upper: The cumulative Pop III and Pop II stars in three simulations. The solid lines represent the Pop II star while the dashed lines represent the Pop III star. Bottom: The Pop III and Pop II star formation rate density (SFRD) from $z=20$ to $z=10$ in three simulations. The points (dark blue: donnan2023, orange: willott2024, green: pg2023, pink: mcleod2024) represent the SFRD derive from the observed UV luminosity function. The green solid and dashed lines represent the simulations results about Pop II and Pop III SFRD in wise12.
• Figure 3: The gas surface density, LW radiation intensity ($J_{21}$), and the ratio of the LW intensity to the critical threshold for ${\rm H_2}$ cooling suppression for the two most massive subhalos in the IC0 simulation at $z=10$. The black dashed circles represent the radius containing half of the total mass, and black points indicate star particles. The third panel displays $\log\left( (J_{21}/n)/(J_{21}/n)_{\rm crit} \right)$; regions with values $>0$ indicate where the LW background is strong enough relative to the density to dissociate ${\rm H_2}$ and suppress cooling. This visualization explicitly confirms that the star-forming neighbor (bottom) generates a strong LW flux that irradiates the massive quiescent halo (top), preventing gas cooling and star formation in its center.
• Figure 4: The gas phase diagram of number density and temperature for all gas ( upper), metal-poor gas ( middle, defined by $Z/Z_{\odot}<10^{-4}$) and metal-rich gas( bottom, defined by $Z/Z_{\odot}\ge10^{-4}$) at z=10. Each row represents the results from the same simulation.
• Figure 5: The time evolution of the metal-rich gas ($Z/Z_{\odot}>10^{-4}$) volume filling factor from $z=20$ to $z=10$.