WARPFIELD 2.0: Feedback-regulated minimum star formation efficiencies of giant molecular clouds

TL;DR

This paper introduces WARPFIELD 2.0, an improved simulation tool for studying stellar feedback in giant molecular clouds, revealing that feedback regulates star formation efficiencies mainly based on cloud surface density.

Contribution

WARPFIELD 2.0 enhances previous models with better thermal and fragmentation treatments, providing new insights into feedback effects on GMCs across various conditions.

Findings

Star formation efficiency needed to destroy GMCs is 1-6%.

Feedback alone explains low star formation efficiencies in GMCs.

Massive, steep-profile clouds are more resistant to feedback.

Abstract

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. In a recent paper, 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 of the gas, which we now make publically 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 $\epsilon_{\mathrm{min}}$, i.e. the star formation efficiency above which the cloud is destroyed by feedback and further star formation is shut off, is mainly set by the average cloud surface density. A star formation efficiency of 1-6 % is generally sufficient to destroy a GMC. We also find star formation efficiencies per free-fall time $\epsilon_{\mathrm{ff}} \sim 0.3$ %, in good agreement with recent observations. Our results imply that stellar feedback alone is sufficient to explain the low observed star formation efficiencies of GMCs. Finally, we show that very massive clouds with steep density profiles - possible proxies of the giant clumps observed in galaxies at $z \approx 2$ - are more resilient to feedback than typical GMCs, with $\epsilon_{\mathrm{min}}$ between 1 and 12 %.