Mass–age plane for a simulated population of clusters based on Model 1. This has a power-law initial mass function, a constant formation rate, and sudden mass-dependent disruption with τ _* = 5 × 10 ⁷ yr and k = 0.62 in Equation (7). The solid line is the approximate upper limit for stellar contamination ( L = 3 × 10 ⁵ L _☉), while the dashed line indicates the age at which clusters are destroyed. The number of clusters in the simulated population above the solid line is approximately the same as in the real Antennae population. The region marked D here is empty, in contrast to the same region of Figure 2.