Channel maps of C¹⁸O observations (top), free falling disk model shown in Fig. 6 (middle) and residual (bottom panel). The blue contours show the blueshifted emission and the red contours the redshifted emission. Number labels on the top of each panel indicate the velocity of that channel. Channels are binned to a velocity resolution of 0.16 km s^-1 for the blueshifted emission, and 0.33 km s^-1 for the redshifted emission for better display. Contours are in steps of 3σ, 5σ, 10σ, 15σ, 20σ and 25σ for the observations and model channel maps, and − 8σ, − 5σ, − 3σ, 3σ, 4σ, 5σ and 6σ for the residual channel map, where σ = 19 mJy beam^-1.