http://arxiv.org/abs/1910.09554
Supernovae (SNe) drive multiphase galactic outflows, impacting galaxy formation; however, cosmological simulations mostly use \textit{ad hoc} feedback models for outflows, making outflow-related predictions from first principles problematic. Recent small-box simulations resolve individual SNe remnants in the interstellar medium (ISM), naturally driving outflows and permitting a determination of the wind loading factors of energy \etaE, mass \etam, and metals \etaZ. In this Letter, we compile small-box results, and find consensus that the hot outflows are much more powerful than the cool outflows: (i) their energy flux is 2-20 times greater, and (ii) their specific energy $e_{s,h}$ is 10-1000 times higher. Moreover, the properties of hot outflows are remarkably simple: $e_{s,h} \propto \eta_{E,h}/\eta_{m,h}$ is almost invariant over four orders of magnitude of star formation surface density. Also, we find tentatively that $\eta_{E,h}/\eta_{Z,h} \sim$ 0.5. If corroborated by more simulation data, these correlations reduce the three hot phase loading factors into one. Finally, this one parameter is closely related to whether the ISM has a “breakout” condition. The narrow range of \esh\ indicates that hot outflows cannot escape dark matter halos with log $M_{\rm{halo}}\ [M_\odot] \gtrsim 12$. This mass is also where the galaxy mass-metallicity relation reaches its plateau, implying a deep connection between \textit{hot} outflows and galaxy formation. We argue that hot outflows should be included explicitly in cosmological simulations and (semi-)analytic modeling of galaxy formation.
M. Li and G. Bryan
Wed, 23 Oct 19
52/64
Comments: 9 pages, 4 figures, submitted to ApJL