Top panel: as mentioned in Sect. 3.3, the slit length was limited by the position of the arcs, hence producing poor sky subtraction. Left: observed spectrum of arc A (black continuous line). In gray we depict a starburst template from Kinney et al. (1996) shifted at z = 1.628, and we indicate a possible [OII]λ3727 emission line, and some sky lines, in blue (see Sect. 3.3). Right: observed spectrum of arc C (black continuous line), as before we depicted in gray the starburst template from Kinney et al. (1996), but shifted at z = 1.02. We indicated some characteristic emission lines, along with the sky lines in blue, but we omit for clarity the labels of the last lines. Bottom panel: two-dimensional spectra of arc A (with a color bar in arbitrary units). We note the [OII]λ3727 emission line. Below, we show the two-dimensional spectra of arc C, with two emission lines clearly identified: [OII]λ3727, and [OIII]λ4958.9.