Position-velocity diagram of the ratio of the low-resolution ¹³CO(2–1) and ¹²CO(2–1) brightness temperatures along the jet axis of IC 5063 where the data, before taking the ratio, have been averaged over 1.5 arcsec perpendicular to the jet axis. Only pixels for which the error in the ratio is smaller than 0.07 are shown. For the regions in the diagram where the fast outflow is occurring, the values should be regarded as upper limits since no ¹³CO(2–1) emission is detected there. The spatial resolution along the jet axis is 1.̋52.