Outward radial momentum per SN at the end of the PDS phase as a function of ambient density. Uncertainties arise due to the finite spacing of the snapshots and due to the choice of Z_{ej, thr}. At sufficiently high densities, n_H ≳ 0.1 cm⁻³, the momentum input offers a good match to the prediction of simulations of isolated SNRs (Kim & Ostriker 2015; Romano et al. 2024a). On the other hand, at lower densities, the momentum per SN is often lower than expected, with large error bars.