Observational Magnetogasdynamics: 21 Years of HI Zeeman Splitting Measurements...and More
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 typical turbulent Mach number 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 discuss 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 × 104 yr.
Keywordsinterstellar medium magnetic fields
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- Crutcher, R.M., Heiles, C. and Troland, T.H.: 2003, in: E. Falgarone and T. Passot (eds.), Turbulence and Magnetic Fields in Astrophysics,Springer, p. 155.Google Scholar
- Hartmann, D. and Burton, W.B.: 1997, Atlas of Galactic Neutral Hydrogen,Cambridge University Press (LDS).Google Scholar
- Heiles, C. and Kulkarni, S.: 1986, in: G.E. Morfill and M. Scholer (eds.), Physical Processes in Interstellar Clouds, Reidel, Dordrecht, The Netherlands, p. 13.Google Scholar
- Knapp, G.R.: 1991, in: Frontiers of Stellar Evolution, ASP Cont. Ser, Vol. 20, p. 229Google Scholar
- Spitzer, L.: 1978, Physical Processes in the Interstellar Medium,Wiley, p. 143.Google Scholar