Starburst Driven Galactic Superbubbles Radiating to 10 K

Abstract

Our three-dimensional hydro-dynamical simulations of starbursts examine the formation of superbubbles over a range of driving luminosities and mass loadings that determine superbubble growth and wind velocity. From this we determine the relationship between the velocity of a galactic wind and the power of the starburst. We find a threshold for the formation of a wind, above which the speed of the wind is not affected by grid resolution or the temperature floor of our radiative cooling. We investigate the effect two different temperature floors in our radiative cooling prescription have on wind kinematics and content. We find that cooling to $10$ K instead of to $10^4$ K increases the mass fraction of cold neutral and hot X-ray gas in the galactic wind while halving that in warm H$\alpha$. Our simulations show the mass of cold gas transported into the lower halo does not depend on the starburst strength. Optically bright filaments form at the edge of merging superbubbles, or where a cold dense cloud has been disrupted by the wind. Filaments formed by merging superbubbles will persist and grow to $>400$ pc in length if anchored to a star forming complex. Filaments embedded in the hot galactic wind contain warm and cold gas that moves $300-1200$ km s$^{-1}$ slower than the surrounding wind, with the coldest gas hardly moving with respect to the galaxy. Warm and cold matter in the galactic wind show asymmetric absorption profiles consistent with observations, with a thin tail up to the wind velocity.