Spectral variations of Lyman-alpha emission within strongly lensed sources observed with MUSE

TL;DR

This study uses gravitational lensing and MUSE observations to map detailed Lyman-alpha emission structures in high-redshift galaxies, revealing systematic variations in line profiles at sub-kiloparsec scales.

Contribution

It provides the first detailed sub-kpc scale maps of Lyman-alpha line variations in strongly lensed galaxies, uncovering systematic intrahalo spectral shifts and correlations.

Findings

Detected small but significant variations in Lyman-alpha line profiles within halos.

Found a trend of redder line peaks at larger radii in the halos.

Observed a correlation between surface brightness and line shift.

Abstract

We present an analysis of HI Lyman-alpha emission in deep VLT/MUSE observations of two highly magnified and extended galaxies at z=3.5 and 4.03, including a newly discovered, almost complete Einstein ring. While these Lyman-alpha haloes are intrinsically similar to the ones typically seen in other MUSE deep fields, the benefits of gravitational lensing allows us to construct exceptionally detailed maps of Lyman-alpha line properties at sub-kpc scales. By combining all multiple images, we are able to observe complex structures in the Lyman-alpha emission and uncover small (~ 120 km/s in Lyman-alpha peak shift), but significant at > 4 sigma, systematic variations in the shape of the Lyman-alpha line profile within each halo. Indeed, we observe a global trend for the line peak shift to become redder at large radii, together with a strong correlation between the peak wavelength and line width. This systematic intrahalo variation is markedly similar to the object-to-object variations obtained from the integrated properties of recent large samples. Regions of high surface brightness correspond to relatively small line shifts, which could indicate that Lyman-alpha emission escapes preferentially from regions where the line profile has been less severely affected by scattering of Lyman-alpha photons.