The energy and momentum input of supernova explosions in structured and ionized molecular clouds

We investigate the early impact of single and binary supernova (SN) explosions on dense gas clouds with three-dimensional, high-resolution, hydrodynamic simulations. The effect of cloud structure, radiative cooling and ionizing radiation from the progenitor stars on the net input of kinetic energy, f kin = E kin/E SN, thermal energy, f therm = E therm/E SN, and gas momentum, f P = P/P SN, to the interstellar medium (ISM) is tested. For clouds with $\bar{n} = 100\;{\rm cm}^{-3}$ , the momentum generating Sedov and pressure-driven snowplough phases are terminated early (∝0.01 Myr) and radiative cooling limits the coupling to f therm ∼ 0.01, f kin ∼ 0.05, and f P ∼ 9, significantly lower than for the case without cooling. For pre-ionized clouds, these numbers are only increased by ∼50 per cent, independent of the cloud structure. This only suffices to accelerate ∼5 per cent of the cloud to radial velocities ≳30 km s−1. A second SN might enhance the coupling efficiencies if delayed past the Sedov phase of the first explosion. Such very low coupling efficiencies cast doubts on many subresolution models for SN feedback, which are, in general, validated a posteriori. Ionizing radiation appears not to significantly enhance the coupling of SNe to the surrounding gas as it drives the ISM into inert dense shells and cold clumps, a process which is unresolved in galaxy-scale simulations. Our results indicate that the momentum input of SNe in ionized, structured clouds is larger (more than a factor of 10) than the corresponding momentum yield of the progenitor's stellar winds.