Simulated spectra of each of the modelled emission lines (fiducial RT model). The total emission is shown in purple, the emission from the central disc in orange, the ISM of the merger components in indigo, and the CGM in yellow. The dotted lines show the multi-component Gaussian line fits performed separately for the spectra of each component. The purple dashed lines show single-Gaussian fits of the total integrated spectra, which we executed with the goal of obtaining an FWHM and peak density value.