Snapshots from the best fitting simulations from group A (left) and B (centre) and GRS observation (right). Shown is the brightness temperature of the ¹³CO line integrated over the radial velocities of ± 8 km s^-1 relative to the radial velocity of the bubble centre. The images also show four sectors used to compare the angular mass distribution (see Sect. 4.3 and Eq. (21)). The plus sign (+) in pictures A and B marks the original expansion centre. Aperture 2, shown in the GRS picture, marks which region from the observed data we used for comparison with simulations.