From raw simulation to synthetic observables for four different systems. From left to right: projected gas column density of the raw simulation, with dots indicating protostars; zero moment maps of the C¹⁸O 2–1 line; line spectra of the two zero moment maps. In the column labelled “no history” the C¹⁸O number densities have been calculated without taking the luminosity history of the central protostar into consideration, while, in the column labelled “history”, the luminosity history has been included. The line spectra have been calculated by integrating over the entire field of view as seen in the moment maps.