CO SLEDs showing different heating mechanisms including CMB heating, PDRs (log(G₀) = 0.0, 1.0, 2.0, 3.0, 4.0), and AGN heating via X-rays at 1.0 kpc and 1.5 kpc. The solid black curve is the best-fit model and the lighter gray lines show the models within the lowest 1% of the χ² values for the different models. Note that the method we employ for isolating the best-fit models is a percentile cut, and it is for this reason that a different number of models are shown for different heating mechanisms.