Ratio of CO(5–4) to CO(2–1), a proxy for gas excitation, as a function of specific star formation rate. Our sample is shown with red circles (non mergers) and stars (mergers) and is compared to literature samples of local star-forming galaxies (blue pentagons), (U)LIRGs (blue squares), high-redshift main-sequence galaxies (cyan circles), and high-redshift SBs (cyan squares; Liu et al. 2021). The companions of ID83492 are shown as brown circles. For post-SBs without CO(2–1) observations, empty symbols indicate a pseudo CO(2–1) estimated from the CO(3–2) assuming the average local post-SBs R₃₂ = 0.62 ratio (French et al. 2023). Large symbols indicate the population averages (see Sect. 4.1). A fit to the literature samples (solid gray line) with its scatter (shaded area) from Valentino et al. (2020) is shown and extrapolated toward lower sSFR (dashed gray line).