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Feedback in Clouds II: UV Photoionisation and the first supernova in a massive cloud

Molecular cloud structure is regulated by stellar feedback in various forms. Two of the most important feedback processes are UV photoionisation and supernovae from massive stars. However, the precise response of the cloud to these processes, and the interaction between them, remains an open question. In particular, we wish to know under which conditions the cloud can be dispersed by feedback, which in turn can give us hints as to how feedback regulates the star formation inside the cloud. We perform a suite of radiative magnetohydrodynamic simulations of a 10^5 solar mass cloud with embedded sources of ionising radiation and supernovae, including multiple supernovae and a hypernova model. A UV source corresponding to 10% of the mass of the cloud is required to disperse the cloud, suggesting that the star formation efficiency should be on the order of 10%. A single supernova is unable to significantly affect the evolution of the cloud. However, energetic hypernovae and multiple supernovae are able to add significant quantities of momentum to the cloud, approximately 10^{43} g cm/s of momentum per 10^{51} ergs of supernova energy. This is on the lower range of estimates in other works, since dense gas clumps that remain embedded inside the HII region cause rapid cooling in the supernova blast. We argue that supernovae alone are unable to regulate star formation in molecular clouds, and that strong pre-supernova feedback is required to allow supernova blastwaves to propagate efficiently into the interstellar medium