Individual spectral component analysis of the CO line ratios as a function of the gas kinematics for our sample of ULIRGs. We set a detection threshold of 2σ for the flux of each Gaussian component in order to compute the ratios. The top, central, and bottom rows show, respectively, the r₂₁, r₃₁, and r₃₂ plots. Left column: Line ratios as a function of the velocity dispersion, σ_v (line width of the spectral Gaussian component). Middle column: Line ratios as a function of the module of the central velocity of the spectral Gaussian component (|v_cen|), measured with respect to the galaxy’s redshift, reported in Table 1. Right column: Line ratios as a function of the σ_v + |v_cen| parameter. The dashed lines correspond to the best-fit relations obtained from a least squares regression analysis, and the shaded gray areas correspond to the 1σ confidence interval of the fit. The Pearson correlation coefficients and associated p-values are reported at the top-right corner of each plot, although they are less informative than the best fit because they do not take the (large) error bars into account.