Starburst Driven Galactic Superbubbles Radiating to 10 K

TL;DR

This study uses 3D hydrodynamical simulations to explore how starburst-driven superbubbles evolve, influence galactic wind properties, and produce observable filamentary structures at different temperature floors.

Contribution

It provides new insights into the impact of cooling to 10 K on wind composition, filament formation, and the relationship between starburst power and wind velocity.

Findings

Cooling to 10 K increases cold gas and X-ray components in winds.

Cold gas mass in the lower halo is independent of starburst strength.

Filaments can grow beyond 400 pc and exhibit asymmetric absorption profiles.

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.