Sketch of the two different slit positions and slit widths of our three VLT/FORS2 visits of the field of GRB 100628A, overlaid onto the Gemini i-band image. Positions with strong emission lines in the 2D spectra (in the following called blobs) are labelled with small circles and numbered (numbers larger than 4 refer to the pixel coordinate along the corresponding slit). Blobs 1, 113, and 2 are seen in the 2D spectrum with the slit oriented from south-east to north-west, i.e., when the slit covered objects B1 and A. All other blobs show up in the 2D spectrum with the slit oriented in the other direction. Blobs 1 and 117 might belong to the same emission-line region in galaxy C (see Fig. 1). The same holds for blobs 2 and 3, which might belong to object K. Regions shown in yellow are at a common redshift z = 0.102 ± 0.001, the redshift of galaxy C. Except for object K, all objects shown in pink are either foreground stars (A, B1) or galaxies (D, G, H, I). Object K could be the interacting partner of C.