Sampling and S/N of the flux densities of the z-GAL galaxies. Top panel: signal-to-noise ratio of the z-GAL data split into Herschel 250, 350, and 500 μm flux densities shown in indigo, which varies between 6 and 10; SCUBA-2 850 μm flux density, in orange, which varies between 1.5 and 7; and NOEMA 2 and 3 mm flux densities, which varies between 1 and 9, shown in black. Bottom panel: distribution of the number of millimeter flux data points available for each z-GAL source shown in gray; all sources have at least 2, and up to 10, measurements. The cyan histogram shows the number of millimeter measurements used in the fitting procedure (below 1 mm in the rest-frame; see Sect. 3) with a median of 5 data points sampling the Rayleigh-Jeans of the z-GAL sources. The indigo-lined histogram shows the number of data points with signal-to-noise ratio > 3.