The disk-halo connection and the nature of the interstellar medium

Abstract

We discuss briefly some new results on the nature of the interstellar medium that are specifically concerned with the disk halo interaction. Over the last five years or so it has become clear that the supernovae rate in our Galaxy is spatially clumped and the consequences of such clumping are superbubbles and supershells fed by tens or hundreds of supernovae per shell. These objects evolve and expand rapidly and soon break out of the disk of the Galaxy, feeding the halo with very significant mass, energy, and momentum. As cooling occurs, gas will rain down onto the disk of the Galaxy completing the cycle.

Here we sketch out the basic flow of physical quantities from disk to halo and vice versa. Some of the many implications are noted including aspects of dynamo theory, quasar absorption lines, the theory of galactic coronae, and the nature of the X-ray background. The essential difference here with the McKee-Ostriker (1977 theory is that the filling factor of the hot gas in the disk is significantly less than unity.