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

, , , , , and .
(2016)cite arxiv:1612.05635Comment: Submitted to MNRAS; 16 pages, 6 figures.

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 ($10^2 M_ødot\,pc^-2$) and extreme ULIRG environments ($10^4 M_ødot\,pc^-2$) 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 ($\epsilon_ff$) and integrated ($\epsilon_int$) 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 $\epsilon_int$, as suggested by analytic force balance arguments from previous works. Furthermore, SFE eventually saturates to $\sim1$ at high surface density, with very good agreement across different spatial scales. We also find a roughly proportional relationship between $\epsilon_ff$ and $\epsilon_int$. 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 $\epsilon_ff$ also contradicts star formation models in which $\epsilon_ff 1\%$ universally, including popular subgrid models for galaxy simulations.

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