ISM -- Oral Presentation
Phases and Processes in The ISM
Bruce Elmegreen, IBM Watson Research Center
Observations with the three Great Observatories reveal the
intricacy of the phase structure of the ISM. Galaxy-scale maps of
molecules, atoms, and dust, all with a wide range of temperatures,
suggest heat sources primarily from starlight, supersonic expansions,
and cosmic rays. ISM motions have similar energy sources, in addition to
self-gravity and galactic scale processes like shear, spiral waves, and
interactions. The structure of the ISM is mostly determined by the
motions, and is therefore a superposition of cavities and shells from
the expansions, along with spiral and globular clouds from a combination
of shear, self-gravity, and spiral arm shocks. There is also a pervasive
fractal hierarchy of cloudy structure from supersonic turbulence wherever
the more directed forces are not dominant. The connections between these
ISM phases and star formation will be discussed.