Detailed analysis of the Ly-α emission line detection. The top panel shows the blow up of the region centered on the Ly-α emission at 6873.45 Å  (dashed line), corresponding to 1215.67 Å  in the emitter rest frame. The central panel shows the corresponding signal-to-noise ratio. The bottom panel reports the counts from the sky (blue line) and for the sky+object (red line). The position of the Ly-α emission in the 2D spectrum (shown in both panels), is marked by a circle and has an offset with respect to the afterglow continuum (corresponding to 0.3′′; see Sect. 2.2.3 for details).