Feedback in Clouds II: UV photoionization 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 photoionization 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 10⁵ solar mass cloud with embedded sources of ionizing radiation and supernovae, including multiple supernovae and a hypernova model. A UV source corresponding to 10 per cent of the mass of the cloud is required to disperse the cloud, suggesting that the star formation efficiency should be of the order of 10 per cent. 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 10⁴³ g cm s^-1 of momentum per 10⁵¹ erg of supernova energy. We argue that supernovae alone are unable to regulate star formation in molecular clouds. We stress the importance of ram pressure from turbulence in regulating feedback in molecular clouds.