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M. A. Avillez, J. Ballesteros-Paredes, M.-M. Mac Low (American Museum of Natural History)
Large scale modelling of the interstellar gas in the disk and halo has been carried out with a three-dimensional hydrodynamical code that uses adapted mesh refinement combined with message passing interface calls. The model includes a gravitational field provided by the stars in the disk, an ideal-gas equation of state, and an approximation for the cooling curve, assuming collisional ionization equilibrium. Supernovae are set up both isolated and in associations, in a manner compatible with observations.
Once disrupted by the explosions, the disk never returns to its initial state, regardless of the initial vertical distribution of the disk gas, provided enough supernovae occur. Instead a thin HI disk forms in the Galactic plane, and, above and below, a thick inhomogeneous gas disk forms, with scale heights in HI of 500 pc and in HII of 1 kpc. The upper parts of the thick HII disk form the disk-halo interface, where a large scale fountain is set up by hot ionized gas escaping in a turbulent convective flow. The calculations also show the formation of HI clouds in both the disk and halo. These are dynamical objects with a two-phase structure composed of a cold core surrounded by warmer gas. The disk is populated by worms, bubbles, superbubbles and chimneys. Chimneys in the simulations have widths of approximately 120 pc. They inject high temperature gas directly from the Galactic disk into the halo, breaking through the warm neutral and ionized layers that compose the thick disk. Mushroom-shaped structures are also seen in the simulations, as have recently been observed. We identify them as tracers of buoyant flow in the thick disk
The author(s) of this abstract have provided an email address for comments about the abstract: mavillez@amnh.org