Turbulent Structure of a Stratified Supernova‐driven Interstellar Medium

To study how supernova feedback structures the turbulent interstellar medium,we construct 3D models of vertically stratified gas stirred by discretesupernova explosions, including vertical gravitational field and parametrizedheating and cooling. The models reproduce many observed characteristics of theGalaxy such as global circulation of gas (i.e., galactic fountain) and theexistence of cold dense clouds in the galactic disk. Global quantities of themodel such as warm and hot gas filling factors in the midplane, mass fractionof thermally unstable gas, and the averaged vertical density profile arecompared directly with existing observations, and shown to be broadlyconsistent. We find that energy injection occurs over a broad range of scales.There is no single effective driving scale, unlike the usual assumption foridealized models of incompressible turbulence. However, >90% of the totalkinetic energy is contained in wavelengths shortward of 200 pc. The shape ofthe kinetic energy spectrum differs substantially from that of the velocitypower spectrum, which implies that the velocity structure varies with the gasdensity. Velocity structure functions demonstrate that the phenomenologicaltheory proposed by Boldyrev is applicable to the medium. We show that it can bemisleading to predict physical properties such as the stellar initial massfunction based on numerical simulations that do not include self-gravity of thegas. Even if all the gas in turbulently Jeans unstable regions in oursimulation is assumed to collapse and form stars in local freefall times, theresulting total collapse rate is significantly lower than the value consistentwith the input supernova rate. Supernova-driven turbulence inhibits starformation globally rather than triggering it.Comment: 15 pages, 11 figures, submitted to ApJ; corrected typo