A Study of the Vertical Motion of Supernova Remnant Bubbles in the Interstellar Medium Drawn from the Results of Three-Dimensional MHD Simulations

摘要

In order to determine the circumstances under which isolated SNRs are capableof rising into and enriching the thick disk and galactic halo, simulations ofsupernova remnants are performed with the FLASH magnetohydrodynamic code. Weperformed simulations in which the interstellar magnetic field is parallel toor perpendicular to the galactic plane as well as a simulation without amagnetic field. The ambient gas density distribution and gravitationalpotential are based on observations of our galaxy. We evolve the remnants toages of roughly 10,000,000 years. For our simulation without a magnetic field,we compare the evolution of the hot bubble's velocity with the velocityevolution calculated from the buoyant and drag accelerations. We foundsurprisingly small vertical velocities of the hot gas, from which we estimatedthe drag coefficient to be ten for the non-magnetic simulation. Although wefound little buoyant motion of the hot gas during the remnant's lifetime, wefound rapid vertical motion of the associated cool dense gas near the end ofthe remnants life. This motion deformed the remnant into a mushroom cloudstructure similar to those found in previous simulations. The simulation inwhich we have a 4 micro-Gauss magnetic field parallel to the galactic mid-planeshows a dramatically elongated bubble parallel to the magnetic field. Themagnetic field pins the supernova remnant preventing it from rising. In thesimulation with the 4 micro-Gauss magnetic field perpendicular to the midplanethe hot bubble rises more, indicating that having the magnetic field in thesame direction as the gravitational force enhances the rise of the bubble.