# The VANDELS survey: the role of ISM and galaxy physical properties on the escape of Ly{\alpha} emission in z $\sim$ 3.5 star-forming galaxies

## TL;DR

This study analyzes the physical properties of 52 Lyα emitting galaxies at z~3.5, revealing how ISM kinematics and HI column density influence Lyα escape, spatial distribution, and correlations with galaxy characteristics.

## Contribution

It provides new insights into the role of ISM outflows and HI column density in Lyα emission and spatial extension, supported by observational correlations in a well-defined galaxy sample.

## Key findings

- Brighter Lyα emission correlates with lower mass, less dust, and bluer UV slopes.
- Galaxies with higher ISM outflow velocities have smaller Lyα velocity shifts.
- Higher HI column densities are associated with more extended Lyα emission profiles.

## Abstract

We investigate the physical properties of a sample of 52 Ly{\alpha} emitting galaxies in the VANDELS survey, with particular focus on the role of kinematics and neutral hydrogen column density in the escape and spatial distribution of Ly{\alpha} photons. For these galaxies, we derive different physical properties and characterize the Ly{\alpha} emission in terms of kinematics, EW, FWHM and spatial extension and then estimate the velocity of the neutral outflowing gas. We reproduce some of the well known correlations between Ly{\alpha} EW and stellar mass, dust extinction and UV \b{eta} slope, in the sense that the emission line appears brighter in lower mass, less dusty and bluer galaxies. We do not find any correlation with the SED-derived star formation rate, while we find that galaxies with brighter Ly{\alpha} tend to be more compact both in UV and in Ly{\alpha}. Our data reveal a new interesting correlation between the Ly{\alpha} velocity and the offset of the inter-stellar absorption lines with respect to the systemic redshift, in the sense that galaxies with larger inter-stellar medium (ISM) out-flow velocities show smaller Ly{\alpha} velocity shifts. We interpret this relation in the context of the shell-model scenario, where the velocity of the ISM and the HI column density contribute together in determining the Ly{\alpha} kinematics. In support to our interpretation, we observe that galaxies with high HI column densities have much more extended Ly{\alpha} spatial profiles, a sign of increased scattering. However, we do not find any evidence that the HI column density is related to any other physical properties of the galaxies, although this might be due in part to the limited range of parameters that our sample spans.