¹²CO line ratios. Left panels: L′ line luminosity ratios, r_ij/lm between the transitions ¹²CO(i − j)/¹²CO(l − m). The red long-dashed vertical lines mark the median z-GAL ratios (Table 1). The dotted light-blue vertical lines represent the ratios reported for SMGs by CW13; the short dash orange lines the H21 SMG ratios; and the dot-dash green lines the B20 line ratios of less luminous galaxies, complementary to the z-GAL sample. Right panels: Observed intensity I ratios, R_ij/lm; the red long-dashed vertical lines mark the median values.