Lyman-alpha Pressure Strongly Enhances Pre-Supernova Feedback at Cosmic Dawn: The First Multi-Dimensional Lyman-alpha Radiation Hydrodynamics Simulations

Abstract

The dynamical role of Lyman-$α$ (Ly$α$) radiation pressure feedback has been debated for nearly a century, with recent analytical and 1D numerical studies highlighting its potential dominance over other stellar feedback processes at Cosmic Dawn. Despite this, no multi-dimensional Ly$α$ radiation hydrodynamics (RHD) simulations have been performed to date. In this paper, we present the first 2D Ly$α$ RHD simulations using Lydion, an RHD code with a novel M1 moment method for Ly$α$ transfer, and self-consistent dust dynamics. Lydion yields a $\sim \mathcal{O}(100) \,\times$ speed-up compared to Monte Carlo radiative transfer in simple benchmarks, making 2D Ly$α$ RHD feasible. We perform simulations of star clusters and isolated stars embedded in dense, metal-poor ($Z/Z_\odot \leq 0.01$) clouds, and find that Ly$α$ feedback dramatically boosts outflows and dominates over feedback from direct and infrared radiation pressure. Ly$α$ leakage through lower-column density channels, Doppler shifts, and Ly$α$ photon destruction, while important, cannot prevent the build-up of strong Ly$α$ radiation pressure in H II regions, leading to radiative forces $\sim (2 - 16) \times L_{\rm bol}/c$, and Ly$α$ force multipliers $M_{\rm F} \sim 10-60$. Ly$α$ feedback may not preclude efficient star formation, but raises the threshold gas surface density for this to occur. We conclude that nearly all galaxy and star formation simulations are currently missing the strongest source of radiation pressure feedback in dense and metal-poor environments.