Spitzer channel-2 postage stamps (30″  ×  30″, with 2″ angular resolution) in grey scale (from 0.35 to 0.6 MJy sr⁻¹) of the eight ALMA fields. White contours show the Herschel 250 μm surface brightness (from 0.01 Jy beam⁻¹ in 0.005 Jy beam⁻¹ or 1σ steps). Green contours represent the ALMA surface brightness (from 0.12 mJy beam⁻¹ in 0.06 mJy beam⁻¹ or 1σ steps). The detected ALMA galaxies are labelled with 1″ radius magenta circles, their photometric redshifts derived in Sect. 5 (or spectroscopic redshifts for ALMA IDs 3 and 8, Sect. 6) are given in white, and the ALMA fields are numbered in blue.