Left: 1.17 mm continuum map displayed in the flux range −2σ − 20σ. The black ellipse in the lower left indicates the beam FWHM. Sources with S/N > 4.2 are indicated with their ID number in Table 1. The IDs of z = 3.09 protocluster members confirmed by spectroscopy are highlighted in cyan. Sources with non-zero values at z = 3.09 in their photometric redshift probability functions (A34, A47, A49, and A55) are in yellow. The white contour indicates a primary beam response of 20%. The coloured contours show the areas with spectroscopic coverage from VLT/MUSE (green), the Umehata et al. (2019) shallow CO mosaic (orange), and deep CO observations of A1 and A4 (red).