Lyman-α feedback prevails at Cosmic Dawn: implications for the first galaxies, stars, and star clusters

Abstract

Radiation pressure from Lyman-α (Lyα) scattering is a potentially dominant form of early stellar feedback, capable of injecting up to ∼ 100 × more momentum into the interstellar medium (ISM) than ultraviolet continuum radiation pressure and stellar winds. Lyα feedback is particularly strong in dust-poor environments and is thus especially important during the formation of the first stars and galaxies. As upcoming galaxy formation simulations incorporate Lyα feedback, it is crucial to consider processes that can limit it to avoid placing Lambda-cold dark matter in apparent tension with recent JWST observations indicating efficient star formation at Cosmic Dawn. We study Lyα feedback using a novel analytical Lyα radiative transfer solution that includes the effects of continuum absorption, gas velocity gradients, Lyα destruction (e.g. by 2p → 2s transitions), ISM turbulence, and atomic recoil. We verify our solution for uniform clouds using extensive Monte Carlo radiative transfer (MCRT) tests, and resolve a previous discrepancy between analytical and MCRT predictions. We then study the sensitivity of Lyα feedback to the aforementioned effects. While these can dampen Lyα feedback by a factor ≤ few × 10, we find it remains ≥ 5 − 100 × stronger than direct radiation pressure and therefore cannot be neglected. We provide an accurate fit for the Lyα force multiplier MF, suitable for implementation in subgrid models for galaxy formation simulations. Our findings highlight the critical role of Lyα feedback in regulating star formation at Cosmic Dawn, and underscore the necessity of incorporating it into simulations to accurately model early galaxy evolution.