Diversity of CO SLEDs for main-sequence and starburst galaxies. Blue filled circles and open squares indicate the main-sequence and starburst galaxies with detected CO (5 − 4) and CO (2 − 1) lines from our ALMA follow-up, normalized to the mean CO (2 − 1) flux for the main-sequence sample. The open red circles and squares indicate the mean fluxes for main-sequence, starburst (ΔMS ≥ 3.5), and extreme starburst (ΔMS ≥ 7) objects. The solid line shows the line ratios for a fully thermalized case. The gray shaded area marks the model by Narayanan & Krumholz (2014) for unresolved observations within Σ_SFR = 1−10 M_⊙ yr⁻¹ kpc⁻². The long dashed line indicates the simulations from Bournaud et al. (2015). The dotted line traces the empirical model by Papadopoulos et al. (2012). The dashed-dotted line points at the analytical model by Vollmer et al. (2017).