Numerical Simulations of Galactic Outflow and Inflow Phenomena

Abstract

The recent progress of numerical studies on outflow phenomena from the galactic disk to the halo is summarized. Firstly, a galactic-scale outflow is considered. If the high-velocity cloud is formed from the radiatively cooled gas, which was originally ejected from the disk as a hot gas, the temperature and density at the base of the halo should be ~ 106 K and 10–3 cm–3. Next, recent results of numerical simulations of the evolution of superbubbles, through which hot gas flows out to the halo, are reviewed. In the case of a thin disk whose density scale height is H ≃ 100 pc, the shell begins to be accelerated upwardly after several dynamical time scales. After that, the polar cap of the shell is broken and the hot gas flows away into the halo. In the case of a thick disk (H ≃ 500 pc) or a magnetized disk with a magnetic field parallel to the disk (B ≃ 5μG), the shell is not accelerated and never shows blow-out.