Lyman alpha emission from the first galaxies: Signatures of accretion and infall in the presence of line trapping

TL;DR

This paper uses cosmological simulations to study Lyman alpha emission from early galaxies, revealing how gas infall and line trapping produce observable signatures that can be detected by future telescopes like JWST.

Contribution

It introduces a detailed simulation model of atomic hydrogen and line trapping effects to explain Lyman alpha emission from first galaxies, linking gas dynamics to observable signals.

Findings

Lyman alpha luminosity reaches ~10^44 erg/s at z=4.7

Emission mainly originates from the halo envelope, not the center

Predicted fluxes are detectable by JWST

Abstract

The formation of the first galaxies is accompanied by large accretion flows and virialization shocks, during which the gas is shock-heated to temperatures of $\sim10^4$ K, leading to potentially strong fluxes in the Lyman alpha line. Indeed, a number of Lyman alpha blobs has been detected at high redshift. In this letter, we explore the origin of such Lyman alpha emission using cosmological hydrodynamical simulations that include a detailed model of atomic hydrogen as a multi-level atom and the effects of line trapping with the adaptive mesh refinement code FLASH. We see that baryons fall into the center of a halo through cold streams of gas, giving rise to a Lyman alpha luminosity of at least $\rm 10^{44} erg s^{-1}$ at $\rm z=4.7$, similar to observed Lyman alpha blobs. We find that a Lyman alpha flux of $\rm 5.0\times 10^{-17} erg cm^{-2} s^{-1}$ emerges from the envelope of the halo rather than its center, where the photons are efficiently trapped. Such emission can be probed in detail with the upcoming James Webb Space Telescope (JWST) and will constitute an important probe of gas infall and accretion.