CO emission on and above the main sequence. L′ [K km s⁻¹ pc²]/L_IR [L_⊙] for CO (2 − 1) (top left), CO (5 − 4) (top right), CO (7 − 6) (bottom right), and the / ratio (bottom left) as a function of the distance from the main sequence. In every panel, the sample of main-sequence galaxies and starbursts at z ∼ 1.3 presented here is marked by blue filled circles and open black squares. Open blue triangles and purple stars indicate other distant MS galaxies and SBs (at z = 0.5−0.8 from the PHIBSS-2 survey of CO (2 − 1), Freundlich et al. 2019; at z ∼ 1.5 from D15, Silverman et al. 2018a,b). Open red circles signpost local spirals (Leroy et al. 2008; Kennicutt et al. 2011; Dale et al. 2012, 2017, Liu et al., in prep.). The red solid line and the shaded area indicate the main sequence within ∥ΔMS∥< 3.5 as parameterized by Sargent et al. (2014). The tracks and the shaded areas mark the best-fit models from the linear regression analysis and their 95% confidence interval when modeling the following samples: solid dark blue line: our galaxies at z ∼ 1.3, excluding the strongest outlier above the main sequence; dashed dark blue line: PHIBSS-2 galaxies at z = 0.5−0.8; dotted-dashed dark blue line: local spirals; solid light blue line: all samples available (see Table 3 for the parameters). The dashed and solid red lines in the top left panel show the tracks for the two-mode star formation model by Sargent et al. (2014) at z = 0.5 and 1.5 and for M_⋆ = 10^10.7 M_⊙, the median mass of both the PHIBSS-2 and our sample. The median error bars for each sample are displayed in the panel.