When Feedback Fails: The Scaling and Saturation of Star Formation Efficiency

Grudić et al., available on arXiv.

Abstract: We present a suite of 3D multi-physics MHD simulations following star formation in isolated turbulent molecular gas disks ranging from 5 to 500 parsecs in radius. These simulations are designed to survey the range of surface densities between those typical of Milky Way GMCs (~10^2 Msun pc^-2}) and extreme ULIRG environments (~10^4 Msun pc^-2) so as to map out the scaling of star formation efficiency (SFE) between these two regimes. The simulations include prescriptions for supernova, stellar wind, and radiative feedback, which we find to be essential in determining both the instantaneous (eps_ff) and integrated (eps_int) star formation efficiencies. In all simulations, the gas disks form stars until a critical stellar mass has been reached and the remaining gas is blown out by stellar feedback. We find that surface density is a good predictor of eps_int, as suggested by analytic force balance arguments from previous works. Furthermore, SFE eventually saturates to ~1 at high surface density, with very good agreement across different spatial scales. We also find a roughly proportional relationship between eps_ff and eps_int. These results have implications for star formation in galactic disks, the nature and fate of nuclear starbursts, and the formation of bound star clusters. The scaling of eps_ff also contradicts star formation models in which eps_ff~1% universally, including popular subgrid models for galaxy simulations.