CO(3−2)/CO(1−0), CO(4−3)/CO(1−0) and CO(4−3)/CO(3−2) flux ratios. Values exceeding 9, 16 and 1.78 for CO(3−2)/CO(1−0), CO(4−3)/CO(1−0) and CO(4−3)/CO(3−2) respectively, indicate the presence of optically thin gas. First row: flux ratios in the velocity range of the entire disk. Second row: flux ratios in disk velocities that show high excitation close to the nucleus. Third row: flux ratios in a sub-range of the velocities that shows excitation in the southern tail-like structure.