2006/10/05 by D. S. Wiebe, W. D. Watson
Chemistry · Physics and Astronomy · #Anisotropy #Astrophysics and Star Formation Studies #Chemistry #Computational physics #Galaxies: Formation, Evolution, Phenomena #Linear polarization #Magnetic field #Magnetohydrodynamic drive #Magnetohydrodynamic turbulence #Magnetohydrodynamics #Mechanics #Optics #Physics #Polarization (electrochemistry) #Quantum mechanics #Radiative transfer #Scattering #Spectral line #Stellar, planetary, and galactic studies #Stokes parameters #Turbulence #Zeeman effect #astro-ph
paper · pdf · doi:10.1086/509883
published as Astrophys.J.655:275-284,2007 · ApJ, accepted
arxiv created 2006/10/05 · openalex publication_date 2007/01/20 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
The anisotropy of velocities in MHD turbulence is demonstrated explicitly by calculating the velocity gradients as a function of direction in representative simulations of decaying turbulence. It follows that the optical depths of spectral lines are anisotropic when there is MHD turbulence and that this anisotropy influences the polarization characteristics of the emergent radiation. We calculate the linear polarization that results for the microwave lines of the CO molecule in star-forming gas and show that it is comparable to the polarization that is observed. This and our earlier result—that the anisotropy of MHD turbulence may be the cause for the absence of the Zeeman π-components in the spectra of OH mainline masers—are the first demonstrations of the occurrence of anisotropy in the optical depths caused by MHD turbulence. A nonlocal approximation is developed for the radiative transfer, and the results are compared with those from a local (LVG) approximation.