Radio observations of HI self-absorption lines can augment our understanding of the cloud structure and content of the local interstellar medium (ISM); in this way, most of the optically determined dark clouds (1(, )<(, )A(,v(, ))<(, )4) in the solar neighborhood are evident. The clouds seem to be principally molecular, but without possessing high enough density to be visible in molecular-line emission. Therefore, optical dark cloud material has not been included in radio morphological studies of the Milky Way or other galaxies. This thesis also attempts to answer the question: Can galactic shocks, which are thought to underlie the spiral structure in many disk galaxies, form and persist in a cloud-dominated ISM which has most of the ISM mass in discrete clouds? An affirmative answer is provided to this question by a cloud/particle model. The model incorporates elements of the density wave and stochastic star formation (via supernovae) mechanisms for a unified picture of spiral structure and star formation in galaxies.
- Pub Date:
- Physics: Astronomy and Astrophysics