On the Turbulent Velocity Dispersion in Molecular Clouds

Details On the Turbulent Velocity Dispersion in Molecular Clouds On the Turbulent Velocity Dispersion in Molecular Clouds

Sep 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999apj...522l.141m&link_type=abstract

The Astrophysical Journal, Volume 522, Issue 2, pp. L141-L144.

Astronomy and Astrophysics

Astronomy

24

Ism: Clouds, Magnetohydrodynamics: Mhd, Turbulence

Scientific paper

We model the ``line width-size relation'' sigma-L^alpha by averaging a power-law spectrum of turbulent motions over a region of size L. This model reproduces the index alpha=0-1 of most line width-size relations observed in molecular clouds, provided that L lies within the range of component wavelengths, the turbulent energy spectrum has power-law index p=1-2, and the spectral components have random relative phases. The relation between p and alpha is independent of the dimensionality of the turbulence. As p increases beyond ~3, alpha approaches unity, departing from the value (p-1)/2 expected in a simpler model, because the velocity profile approaches that of its longest wavelength spectral component. Fixed relative phases, expected for excitation by coherent sources, also yield a power-law line width-size relation but require a much steeper energy spectrum to match observations. If the turbulent spectrum has sharp cutoffs, the slope alpha changes sharply as L goes beyond the range of component wavelengths, approaching alpha=1 for Llambda_max, independent of p. These changes in slope are due to simple properties of sinusoids and offer observational signatures of the extreme turbulent wavelengths in a cloud.

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