Delay-time distribution
= Delay-time distribution
{title2=$\Psi(\tau)$}
The event rate per unit initial stellar mass and per unit delay after <star formation>. An extended <star formation history> produces a rate $R(t)=\int\mathrm{SFR}(t-\tau)\Psi(\tau)d\tau$. Measuring rates versus age in old populations constrains progenitor channels only after accounting for stellar lifetimes, age spreads and selection.