# A gravitationally-boosted MUSE survey for emission-line galaxies at z>~5 behind the massive cluster RCS 0224

## TL;DR

This study uses gravitational lensing and MUSE spectroscopy to analyze a highly magnified galaxy at z=4.88, revealing detailed internal properties, nebular emission, and outflow dynamics, and also identifies high-redshift Lyα emitters.

## Contribution

It provides the first detailed internal analysis of a highly magnified z~5 galaxy with nebular emission and outflows, and introduces a new outflow model with a velocity gradient.

## Key findings

- Detection of widespread nebular CIV emission.
- Observation of a bright Lyα halo with uniform wind profile.
- Identification of 14 high-redshift Lyα emitter candidates.

## Abstract

We present a VLT/MUSE survey of lensed high-redshift galaxies behind the z=0.77 cluster RCS0224-0002. We study the detailed internal properties of a highly magnified ({\mu}~29) z=4.88 galaxy seen through the cluster. We detect wide-spread nebular CIV{\lambda}{\lambda}1548,1551{\AA} emission from this galaxy as well as a bright Ly{\alpha} halo with a spatially-uniform wind and absorption profile across 12 kpc in the image plane. Blueshifted high- and low-ionisation interstellar absorption indicate the presence of a high-velocity outflow ({\Delta}v~300 km/s) from the galaxy. Unlike similar observations of galaxies at z=2-3, the Ly{\alpha} emission from the halo emerges close to the systemic velocity - an order of magnitude lower in velocity offset than predicted in "shell"-like outflow models. To explain these observations we favour a model of an outflow with a strong velocity gradient, which changes the effective column density seen by the Ly{\alpha} photons. We also search for high-redshift Ly{\alpha} emitters and identify 14 candidates between z=4.8-6.6, including an over-density at z=4.88, of which only one has a detected counterpart in HST/ACS+WFC3 imaging.