CO(1−0) LF (solid black lines) derived with SPRITZ, compared with observations by Saintonge et al. (2017, red circles), Riechers et al. (2019, green squares), Decarli et al. (2019, pink squares), and Decarli et al. (2020, cyan arrows as upper limits). The grey shaded area contains the propagated errors of the IR LF and errors in the relations used to derive the CO(1−0) luminosity. We also report the models by Popping et al. (2016, dashed magenta lines) and Popping et al. (2019b, dash-dotted blue line). Gr14 and Sa14 refer to the relations by Greve et al. (2014) and Sargent et al. (2014), respectively.