X_CO estimated from Eq. (8) versus I_CO in the top panel (250 pc resolution); X_CO from Eq. (14) in the middle (40 pc resolution); and from Eq. (15) in the lower (40 pc resolution). Also shown as dark-gray dot-dashed lines are the predictions from Narayanan et al. (2012) for the different metallicities of our targets. The 1 kpc trend from Hu et al. (2022), valid for all metallicities, is shown as a light-gray solid line (labeled “1 kpc”). The brown solid (dashed) curves correspond to 0.3 Z_⊙ (Z_⊙) metallicities at 125 pc resolution (top panel) and at 32 pc (middle and lower ones). The 0.3 Z_⊙ curves are the best approximation to the metallicities of our target starbursts. The robust fit in logarithmic space to our data is shown as a dark-yellow line with 1σ excursions by the yellow shaded area; in the lower panels, the dashed dark-yellow line reproduces the 250 pc best fit shown in the upper panel. The trends seen in our data follows the predictions of Hu et al. (2022), in terms of excursion, but we find a steeper slope and an overall higher normalization. We attribute this to the theoretical W₁₀ not being the exact same quantity as observed I_CO, so we approximate W₁₀ as I_CO, which is a better approximation at high I_CO, when X_CO is low, but which is far from true at low I_CO, when X_CO is high. See text for more details.