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Paper: Physical Properties of the Diffuse HI
Volume: 317, Milky Way Surveys: The Structure and Evolution of Our Galaxy
Page: 323
Authors: Heiles, C.
Abstract: We review observations of the physical properties of the diffuse ISM HI components, namely the Cold and Warm Neutral Media (CNM and WNM). There is somewhat more WNM than CNM, and at least half of the WNM is not thermally stable. The CNM has a typical turbulent Mach number of 3. Magnetic fields in the CNM are not as large as expected from the classical flux-freezing argument; neither are magnetic fields always strong enough for the Alfven velocity to equal the turbulent velocity. Nevertheless, they are usually strong enough to put CNM clouds in the magnetically subcritical regime. We identify a probable new source of turbulence for the diffuse ISM. We discus one very cold cloud that has considerable internal turbulence and, because of its extreme thinness (∼ 0.05 pc), a turbulent crossing time of only ∼ 5 x 104 yr.
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