Expansion radius vs. time for models of stellar cluster feedback (WARPFIELD; Rahner et al. 2017) in W49A. t = 0 denotes the formation of the first stellar cluster. Observational constraints on stellar cluster age (A), shell size (B) and extent of W49A (C) are shown in gray. Models 1–3 were computed with molecular gas densities of n = (4.0, 7.5, 2.5) × 10³ cm⁻³, respectively, and a stellar cluster mass of M_* = 1 × 10⁴ M_⊙. Model 4 used a molecular gas density of n = 4.0 × 10³ cm⁻³ and a stellar cluster mass of M_* = 2 × 10⁴ M_⊙. For simplicity, the molecular gas density was assumed to be constant (see text for further discussion). Each model agrees best with the observations at the expansion radius indicated by a filled bar (“Now”), which then defines the elapsed time. The stars with labels “SF” or “SF 1” denote the time of the formation of the first stellar cluster in the model. To put the models into perspective, the observational constraints from the perspective of today (filled bars) on the age of the O/B cluster and the UC H II regions are highlighted by brackets in the top part of the plot (“O/B SF” or “UC H II”). The observational constraints on the O/B star formation in Model 2 (indicated by a yellow arrow) coincides approximately with the formation of the first star cluster in the model. For Model 3, “SF 2” marks the radius and time at which the model reaches the outskirts of W49A (no additional star formation is added to the model at this point).