To be published in New Perspectives on the Interstellar Medium, eds. A. R. Taylor and T. L. Landecker (ASP: San Francisco), submitted 1 November 1998
In this review I focus on how massive stars in the disks of galaxies determine the properties of the ionized, gaseous haloes of star-forming galaxies. I first examine the ionization state of the halo, and conclude that diluted radiation from massive stars, along with a possible secondary heating source such as shocks, appears sufficient to explain the observations. I then look at how single superbubbles evolve, as they must provide one of the main mechanisms for transfer of mass and energy to the halo, as well as opening up lines of sight for ionizing radiation to escape from the disk. Finally, I look at the interactions of superbubbles, as they will rarely evolve in isolation, and describe recent hydrodynamical and MHD simulations of the interstellar medium shaped by multiple superbubbles.
uncompressed postscript (2264 Kb)
MPI Astronomie theory group