2019MNRAS.482.4062H

As part of the SILCC-Zoom project, we present our first sub-parsec resolution radiation-hydrodynamic simulations of two molecular clouds self-consistently forming from a turbulent, multiphase ISM. The clouds have similar initial masses of few 10⁴ M_☉, escape velocities of ∼5 km s^–1, and a similar initial energy budget. We follow the formation of star clusters with a sink-based model and the impact of radiation from individual massive stars with the tree-based radiation transfer module TREERAY. Photoionizing radiation is coupled to a chemical network to follow gas heating, cooling, and molecule formation and dissociation. For the first 3 Myr of cloud evolution, we find that the overall star formation efficiency is considerably reduced by a factor of ∼4 to global cloud values of <10 per cent as the mass accretion of sinks that host massive stars is terminated after <=1 Myr. Despite the low efficiency, star formation is triggered across the clouds. Therefore, a much larger region of the cloud is affected by radiation and the clouds begin to disperse. The time-scale on which the clouds are dispersed sensitively depends on the cloud sub-structure and in particular on the amount of gas at high visual extinction. The damage of radiation done to the highly shielded cloud (MC₁) is delayed. We also show that the radiation input can sustain the thermal and kinetic energy of the clouds at a constant level. Our results strongly support the importance of ionizing radiation from massive stars for explaining the low-observed star formation efficiency of molecular clouds.