Sketch of the proposed model for explaining the ²⁶Al kinematics. In the co-rotating frame chosen here, a spiral arm (solid line) moves anti-clockwise. At its previous location (dashed line), it created large superbubbles (ellipses), blowing out of the disc. The young star clusters (blue stars) at the current spiral arm location feed ²⁶Al (colour gradient in ellipses) into the old superbubbles.