Analysis of synthetic ALMA data cubes. Top row: filtered sky images in C¹⁸O(2−1) for selected channels. Second row: axially symmetric model data cube obtained with DISCKIN. Third row: residuals. Fourth row: point-source residuals after median filtering (see text), with the peaks from 1.0 to 1.6 km s⁻¹ corresponding to the CO bubble and reaching 9 σ significance relative to the scatter in the residuals. Bottom row: symmetric velocity channels relative to the systemic velocity. The data cubes have been averaged into coarse sky pixels, whose solid angle approximates that of the beam, as a means to speed up the DISCKIN optimization.