How stellar feedback regulates star formation and drives outflows

With Phil Hopkins, I have developed an analytic theory for how stellar feedback simultaneously regulates star formation and drives outflows (Hayward & Hopkins 2015). In our model, the equilibrium SFR surface density of a galaxy is set by the requirement that turbulent pressure from stellar feedback supports the gas disk against gravity. Because the ISM is turbulent, a given patch of ISM exhibits sub-patches with a range of surface densities, and patches with surface density below a critical threshold can be accelerated to the escape velocity on a coherence time and thus be blown out as outflows. Importantly, our model predicts that outflows are suppressed in massive galaxies at z < ~1, which enables such galaxies to transition from turbulent, irregular, clumpy disks that experience frequent bursts of star formation and subsequent violent outflows to the stably star-forming, well-ordered disk galaxies with thin molecular gas (and hence young stellar) disks. As shown in the figure, the suppression of outflows predicted by our analytic theory is in striking quantitative agreement with the results of the state-of-the-art FIRE simulations (Muratov et al. 2015). Because these simulations resolve the ISM on ~10-pc scales and include explicit stellar feedback without tunable parameters, the mass outflow rates are predicted, not prescribed. Thus, the agreement between the results of these simulations and the predictions of our theory may indicate that we have uncovered a physical process that is crucial for forming the beautiful disk galaxies that we observe in the local Universe.

© Christopher C. Hayward 2015-2016; all text may not be reproduced without permission. Images and animations can be used for non-commercial purposes with proper attribution. Last updated December 13, 2016.