Magnetic Field Strength from Turbulence Theory. I. Using Differential Measure Approach

Journal Article · 17 August 2022 · The Astrophysical Journal

DOI: https://doi.org/10.3847/1538-4357/ac6877 · OSTI ID:1889994

Lazarian, A.  ^[1]; Yuen, Ka Ho  ^[2]; Pogosyan, Dmitri  ^[3]

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1. University of Wisconsin, Madison, WI (United States); Universidad Bernardo O'Higgins, Santiago (Chile)
2. University of Wisconsin, Madison, WI (United States); Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
3. University of Alberta, Edmonton, AB (Canada); Korea Institute of Advanced Studies, Seoul (Korea, Republic of)

The mean plane-of-sky magnetic field strength is traditionally obtained from the combination of polarization and spectroscopic data using the Davis–Chandrasekhar–Fermi (DCF) technique. However, we identify the major problem of the DCF technique to be its disregard of the anisotropic character of MHD turbulence. On the basis of the modern MHD turbulence theory we introduce a new way of obtaining magnetic field strength from observations. Unlike the DCF technique, the new technique uses not the dispersion of the polarization angle and line-of-sight velocities, but increments of these quantities given by the structure functions. To address the variety of astrophysical conditions for which our technique can be applied, we consider turbulence in both media with magnetic pressure higher than the gas pressure, corresponding, e.g., to molecular clouds, and media with gas pressure higher than the magnetic pressure, corresponding to the warm neutral medium. We provide general expressions for arbitrary admixtures of Alfvén, slow, and fast modes in these media and consider in detail particular cases relevant to diffuse media and molecular clouds. We successfully test our results using synthetic observations obtained from MHD turbulence simulations. We demonstrate that our differential measure approach, unlike the DCF technique, can be used to measure the distribution of magnetic field strengths, can provide magnetic field measurements with limited data, and is much more stable in the presence of induced large-scale variations of nonturbulent nature. Furthermore, our study uncovers the deficiencies of earlier DCF research.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: National Aeronautic and Space Administration (NASA); USDOE Laboratory Directed Research and Development (LDRD) Program; USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: 89233218CNA000001; AC02-05CH11231
• OSTI ID: 1889994
• Report Number(s): LA-UR-22-28277
• Journal Information: The Astrophysical Journal, Journal Name: The Astrophysical Journal Journal Issue: 2 Vol. 935; ISSN 0004-637X
• Publisher: IOP PublishingCopyright Statement
• Country of Publication: United States
• Language: English