2016ApJ...829..130R

Radiation feedback from stellar clusters is expected to play a key role in setting the rate and efficiency of star formation in giant molecular clouds. To investigate how radiation forces influence realistic turbulent systems, we have conducted a series of numerical simulations employing the Hyperion radiation hydrodynamics solver, considering the regime that is optically thick to ultraviolet and optically thin to infrared radiation. Our model clouds cover initial surface densities between {Σ}_{cl,0}∼10–300 {M}_☉ pc^{-2}, with varying initial turbulence. We follow them through turbulent, self-gravitating collapse, star cluster formation, and cloud dispersal by stellar radiation. All our models display a log-normal distribution of gas surface density Σ; for an initial virial parameter α_{vir,0}=2, the log-normal standard deviation is σ_lnΣ=1–1.5 and the star formation rate coefficient ε_ff,{bar}ρ=0.3–0.5, both of which are sensitive to turbulence but not radiation feedback. The net star formation efficiency (SFE) ε_final increases with {Σ}_{cl,0} and decreases with α_{vir,0}. We interpret these results via a simple conceptual framework, whereby steady star formation increases the radiation force, such that local gas patches at successively higher Σ become unbound. Based on this formalism (with fixed σ_lnΣ), we provide an analytic upper bound on ε_final, which is in good agreement with our numerical results. The final SFE depends on the distribution of Eddington ratios in the cloud and is strongly increased by the turbulent compression of gas.