Top (bottom): two-dimensional and 1D spectrum around the Hα ([OIII] 5007 Å) emission line from the counterimage to the radial arc, obtained from GNIRS observations. The 1D spectrum is extracted from a 5 pixel, corresponding to 0.75″, aperture around each line. The secondary peak redward of [OII] visible in the 1D spectrum is due to a cosmic ray that was not properly removed in the data reduction process.