Age distribution of clump associations as a function of relative distance. For each group, the x-axis shows the projected distance of each clump from the reference clump (i.e. the one closest to the galaxy within that group). The y-axis shows the age of the clumps, from which is subtracted the age of the reference clump of each association. Negative values indicate younger clumps farther away from the galaxy (relative to their group). Associations are divided into two categories: in red, those for which the reference clump is older than 100 Myr; in orange, those younger than this age. The best fit of each of the two groups with a constant velocity relation is shown as a continuous line. Lines at constant velocity are indicated as grey dashed lines. They do not appear as straight lines due to the symlog scale on the y-axis.