Overlay of the ¹³CO 1−0 emission observed with ALMA (gray contours) on top of the ¹²CO 1−0 emission observed with ALMA (color scale). Note how the bulk of the ¹³CO 1−0 emission is located outside the dust lane to the west of the nucleus (white contours). Moreover, the ¹³CO 1−0 located in the dust lane does not cover its full extent. The ¹³CO 1−0 contours are the same as in Fig. 3b. North is up, east to the left, and the beams are shown in the lower right corner of the image. The cross marks the position of the phase center of the observations.