# Ly{\alpha} emission from galaxies in the Epoch of Reionization

## TL;DR

This study uses advanced simulations of a high-redshift galaxy to explore how dust, gas, and galaxy structure influence Lyα emission, revealing complex attenuation effects and their implications for galaxy evolution during reionization.

## Contribution

It combines hydrodynamical and radiative transfer simulations to analyze Lyα escape in a prototypical high-redshift galaxy, providing new insights into dust effects and emission variability.

## Key findings

- Lyα escape fractions are low (<1%) with large scatter.
- Dust in clumps significantly attenuates Lyα emission.
- Anti-correlation between Lyα-[CII] velocity shift and Lyα luminosity.

## Abstract

The intrinsic strength of the Ly$\alpha$ line in young, star-forming systems makes it a special tool for studying high-redshift galaxies. However, interpreting observations remains challenging due to the complex radiative transfer involved. Here, we combine state-of-the-art hydrodynamical simulations of 'Althaea', a prototypical Lyman Break Galaxy (LBG, stellar mass $M_{\star}$$\simeq$ $10^{10}{\rm M}_{\odot})$ at $z=7.2$, with detailed radiative transfer computations of dust/continuum, [CII] 158 $\mu$m, and Ly$\alpha$ to clarify the relation between the galaxy properties and its Ly$\alpha$ emission. Althaea exhibits low ($f_\alpha< 1\%$) Ly$\alpha$ escape fractions and Equivalent Widths, EW $\lesssim 6$ Angstrom for the simulated lines of sight, with a large scatter. The correlation between escape fraction and inclination is weak, as a result of the rather chaotic structure of high-redshift galaxies. Low $f_\alpha$ values persist even if we artificially remove neutral gas around star forming regions to mimick the presence of HII regions. The high attenuation is primarily caused by dust clumps co-located with young stellar clusters. We can turn Althaea into a Lyman Alpha Emitter (LAE) only if we artificially remove dust from the clumps, yielding EWs up to $22$ Angstrom. Our study suggests that the LBG-LAE duty-cycle required by recent clustering measurements poses the challenging problem of a dynamically changing dust attenuation. Finally, we find an anti-correlation between the magnitude of Ly$\alpha$-[CII] line velocity shift and Ly$\alpha$ luminosity.