Computational studies of cloudy gaseous galactic disks

Computational studies are carried out to address questions centered on the clumpy cloudy interstellar medium, giant molecular clouds, and star formation in galactic disks. In application to galactic spirals,gaseous self-gravity is found to act on the large scale to enhance the overall collective gravitational field driving the gaseous response and thus help maintain the global spiral structure. On local scales, gaseous self-gravity is found to aid the formation and assembling of massive aggregations of clouds into giant cloud complexes, spurs, and feather-like features. Striking is the local raggedness and patchiness of the computed distribution of gas and young stellar associations. Local spurs, feathers, and secondary features continually break apart and reform as the loosely-associated aggregations and giant complexes of clouds continually disassemble and reassemble over time. Such transient features give rise to local disorder within the global spiral structure and blur the global coherence. Of paramount importance are thenonlinear effects and thedissipative character of thecold cloudy galactic gas component, which largely distinguish it from the stellar component. Without the presence of a cold and dissipative gaseous component, galactic disks would be hard pressed to produce and exhibit sharp, clear-cut spiral structures on global scales.