Comet-like clouds at far-infrared and optical wavelengths - Mach cones and hydrodynamics?

Optical and far-IR studies have been conducted on 14 high Galactic latitude clouds with comet-like or filamentary appearances. Their physical characteristics are deduced and found to be comparable to those of small, low-mass molecular clouds found in the solar neighborhood in recent CO and H I surveys. The morphologies of five of the clouds are found to be consistent with objects moving supersonically through the interstellar medium. These clouds are also active in forming B-type stars in their nuclei where the dynamic pressures are expected to be highest. The filamentary clouds have shapes consistent with subsonic, low Reynolds number hydrodynamics, a feature they may share with the Draco molecular cloud. A simple qualitative scenario is also presented, describing a possible evolutionary link among these clouds as a population. 47 references.