2019MNRAS.483.2547R

Star formation is an inefficient process and in general only a small fraction of the gas in a giant molecular cloud (GMC) is turned into stars. This is partly due to the negative effect of stellar feedback from young massive star clusters. Recently, we introduced a novel 1D numerical treatment of the effects of stellar feedback from young massive clusters on their natal clouds, which we named WARPFIELD. Here, we present version 2 of the WARPFIELD code, containing improved treatments of the thermal evolution of the gas and the fragmentation of the feedback-driven shell. As part of this update, we have produced new cooling and heating tables that account for the combined effects of photoionization and collisional ionization on the cooling rate, which we now make publicly available. We employ our updated version of WARPFIELD to investigate the impact of stellar feedback on GMCs with a broad range of masses and surface densities and a variety of density profiles. We show that the minimum star formation efficiency (SFE) ε_min, i.e. the SFE above which the cloud is destroyed by feedback, is mainly set by the average cloud surface density. An SFE of 1-6 per cent is generally sufficient to destroy a GMC. We also find an SFE per free-fall time ε_ff ∼ 0.3 per cent, in good agreement with recent observations. Our results imply that feedback alone is sufficient to explain the low observed SFE of GMCs. Finally, we show that very massive clouds with steep density profiles - possible proxies of the giant clumps observed in galaxies at z ≃ 2 - are more resilient to feedback than typical GMCs, with ε_min between 1 and 12 per cent.