LVG modeling. Large velocity gradient modeling of the observed CO+[C I] SLEDs for main-sequence (bottom panel), starburst (ΔMS ≥ 3.5, central panel), and extreme starburst galaxies (ΔMS ≥ 7, top panel) from our ALMA survey. The filled symbols show the mean fluxes. The blue and red lines show the low- and high-excitation components of the modeling, with the black solid line indicating their sum. The dotted black line shows the best-fit model with a single component. For reference, we show the CO data for the inner disk of the Milky Way (Fixsen et al. 1999) normalized to the CO (2 − 1) emission of the average main-sequence galaxies as in Fig. 8 (pink open triangles). The upper limits are at 3σ significance.