Superbubble blowout dynamics

Abstract

Multiple supernovae and stellar winds from OB associations carve large holes filled with hot gas in the galactic disk. These superbubbles sweep up H I into cold, thin, dense shells and eventually grow large enough to blow completely out of the galactic H I disk. When superbubbles blow out of the disk, they vent hot gas and supernova energy into the galactic corona. In this paper we use ZEUS, a two-dimensional hydrodyamics code, to model the blowout of a superbubble from exponential and Gaussian models for the vertical density stratification. We compare the results to those from the Kompaneets (thin-shell) approximation. We find that this approximation works very well. We explain the differences between our results and those of other groups who have modeled superbubbles. We find that most of the mass of the shell remains in the plane, with 5% of it accelerating upward. The venting of the hot gas and the stability of the shell depends strongly on the model of the density distribution. We suggest that the low galactic halo actually consists of a froth of merged superbubbles.