2019MNRAS.489.5022C

We present an analysis of H I Lyman αemission 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 αhaloes are intrinsically similar to the ones typically seen in other MUSE deep fields, the benefits of gravitational lensing allow us to construct exceptionally detailed maps of Lyman αline properties at sub-kpc scales. By combining all multiple images, we are able to observe complex structures in the Lyman αemission and uncover small (∼ 120 km s^–1 in Lyman αpeak shift), but significant at > 4 σ, systematic variations in the shape of the Lyman αline 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 αemission escapes preferentially from regions where the line profile has been less severely affected by scattering of Lyman αphotons.