Distribution of the FWHM for all the individual sources identified in the fields of the 137 bright Herschel-selected galaxies of the z-GAL sample and the Pilot Programme (Neri et al. 2020; Stanley et al. 2023) for which spectroscopic redshift were measured – see Tables A.6–A.8. The linewidths of the sources are on average large with a median value for the FWHM of 590 ± 25 km s⁻¹ (Sect. 3.2). For comparison, the distributions of the FWHM for the BEARS sample (Urquhart et al. 2022) and the Herschel-selected galaxies reported in Harris et al. (2012, and references therein) are shown in the red and blue histograms, respectively. The median values of the FWHM are 465 ± 37 km s⁻¹ for the BEARS sample and 485 ± 73 km s⁻¹ for the sample of Harris et al. (2012) – further details are provided in Sect. 3.2.