Field of G073.4−57.5. In the background we show Spitzer 3.6-μm imaging, and the purple circles represent ALMA Band 4 follow-up pointings taken in Cycle 7. The ALMA pointings labelled 1 through 8 were also observed by ALMA in Band 6 in Cycle 2; these pointings were selected as bright, unresolved Herschel-SPIRE sources with red colours (see Kneissl et al. 2019). The ALMA pointings labelled S2-0 through S2-3 were selected as the highest S/N SCUBA-2 850 μm sources (see MacKenzie et al. 2017). Galaxies with only continuum detections in at least one of the ALMA Band 4 and 6 data are indicated by grey circles, while the galaxies in the z  ≈  1.5 structure are shown as blue circles and galaxies in the z  ≈  2.3 structure as orange circles. The two SCUBA-2-selected galaxies for which we detected line emission are shown as red circles, tentatively assigned to z  =  2.6 (see Sect. 3).