Global r_CICO as a function of the velocity dispersion of the gas. Top row: [CI](1–0)/CO(1–0) luminosity ratio as a function of σ_v, CO from the single Gaussian fit (see Sect. 5.1.2, left), and as a function of v_97.7 − v_2.3 velocity interval for CO (right). Bottom row: r_CICO line ratio as a function of OH_max (left) and OH_EQW (right). Sources with direct measurements of both the [CI](1–0) and CO(1–0) lines are plotted using purple crosses. For the other sources (pink diamonds), the CO(1–0) line luminosity was estimated assuming the average CO(2–1)/CO(1–0) luminosity ratio of r₂₁ = 1.1 computed for our sample of ULIRGs. The dashed purple line represents the best fit using a least squares regression analysis, and the shaded gray area corresponds to the 1σ confidence interval of the fit. The Pearson correlation coefficients (ρ) are reported at the upper left corner of the panel with their associated p-values.