Gaseous self gravitational effects in the aggregation of giant molecular clouds: The stability of global spiral structures

Abstract

Self-gravitational effects of the clumpy, cloudy interstellar medium in model spiral galaxies are found to play an important multifold role in the global distribution and morphological appearance of the gas in galactic disks. The results are based on studies via an N-body, cloudparticle computational code developed for the purpose of isolating the role of gaseous self gravity from those of other dominant physical mechanisms and dynamical processes underlying the interstellar medium (Roberts and Stewart, 1987; Roberts, Adler, and Stewart, 1987). Self gravitational effects of the clouds are included by means of Fourier Transform techniques, adapted from those developed by Miller (1976) and Miller and Smith (1979a, b). On the one hand, gas self-gravity acts on the large scale to enhance the overall collective gravitational field driving the gaseous response and thus helps maintain the large-scale order and overall global coherence of the grand design spiral structure. On the other hand, gas self-gravity acts on local scales to aid in the formation and assembling of massive aggregations of clouds into giant cloud complexes, spurs, and feather-like features. These transient features on local scales give rise to local disorder within the global spiral structure and blur the global coherence.