Outline of the oversampled 6  ×  6 regular map with 10′′ spacings of the O₂ 774 GHz observations. At this frequency, the beam of the 3.5 m Herschel telescope has a size of 28′′ (small blue circles). The beam centres for the H- and V-polarisations are separated by 45. Larger (black) circles correspond to the 487 GHz beam positions (44′′; cf. Fig. 1) and as before, north is up and east is to the left. Background image is courtesy of Spitzer IRAC-MIPS (blue: 3.6 μm, green: 8 μm, red: 24 μm).