L_IR-normalised average SLED of the z-GAL sources, compared to high-z SMGs (Carilli & Walter 2013; Yang et al. 2017), local star-forming galaxies (Liu et al. 2015), Arp 220 (Rangwala et al. 2011) and Mrk 231 (van der Werf et al. 2010). In the case of z-GAL data points, if the volume of the values is insufficient for a normal distribution fitting, no uncertainty is shown. Error bars are computed as the Gaussian dispersion of the distribution of each transition (not available for J_up = 7 and 8 because of the small statistics). For comparison, the dark-red error bars on the bottom represent the median uncertainty on based on measurements errors only, as obtained via standard error propagation.