Bursting Bubbles: Feedback from Clustered Supernovae and the Trade-off Between Turbulence and Outflows

Abstract

We present an analytic model for clustered supernovae (SNe) feedback in galaxy disks, incorporating the dynamical evolution of superbubbles formed from spatially overlapping SNe remnants. We propose two realistic outcomes for the evolution of superbubbles in galactic disks: (1) the expansion velocity of the shock front falls below the turbulent velocity dispersion of the interstellar medium in the galaxy disk, whereupon the superbubble stalls and fragments, depositing its momentum entirely within the galaxy disk; or (2) the superbubble grows in size to reach the gas scale height, breaking out of the galaxy disk and driving galactic outflows/fountains. In either case, we find that superbubble breakup/breakout almost always occurs before the last Type II SN (≲40 Myr) in the recently formed star cluster, assuming a standard high-end initial mass function slope, and scalings between stellar lifetimes and masses. The threshold between these two cases implies a break in the effective strength of feedback in driving turbulence within galaxies, and a resulting change in the scalings of, for example, star formation rates with gas surface density (the Kennicutt–Schmidt relation) and the star formation efficiency in galaxy disks.