Left: Spitzer 4.5 μm image in colour and ALMA continuum emission at 87.6 GHz in grey contours. The contour level corresponds to 0.5 Jy beam⁻¹. The radio continuum sources observed with VLA at 4–8 GHz (Medina et al. 2018) are shown as black stars. The rectangles mark the position of the relevant regions also marked in Fig 1. Right: close-up view of the four regions marked with rectangles in the left panel. The circles indicate the position of the ALMA continuum sources (see also Fig. 1). The coloured filled circles correspond to ALMA sources with counterparts at infrared wavelengths(from the catalogue of Willis et al. 2013). The stars indicate the position of VLA sources as in the left panel. Black stars mark those VLA sources with an ALMA counterpart at 87.6 GHz. Grey stars indicate VLA sources with no counterparts in our catalogue.