Measuring magnetization with rotation measures and velocity centroids in supersonic MHD turbulence

Abstract

The interstellar turbulence is magnetized and thus anisotropic. The anisotropy of turbulent magnetic fields and velocities is imprinted in the related observables, rotation measures (RMs), and velocity centroids (VCs). This anisotropy provides valuable information on both the direction and strength of the magnetic field. However, its measurement is difficult especially in highly supersonic turbulence in cold interstellar phases due to the distortions by isotropic density fluctuations. By using 3D simulations of supersonic and sub-Alfvénic magnetohydrodynamic(MHD) turbulence, we find that the problem can be alleviated when we selectively sample the volume-filling low-density regions in supersonic MHD turbulence. Our results show that in these low-density regions, the anisotropy of RM and VC fluctuations depends on the Alfvénic Mach number as ${\mathrm{M}}_{\mathrm{A}}^{-4/3}$. This anisotropy-${\mathrm{M}}_{\mathrm{A}}$ relation is theoretically expected for sub-Alfv 'enic MHD turbulence and confirmed by our synthetic observations of ${}^{12}$CO emission. It provides a new method for measuring the plane-of-the-sky magnetic fields in cold interstellar phases.

16 pages, 12 figures, accepted for publication in ApJ

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Cited by in corpus (5)

• Anisotropies in Compressible MHD Turbulence: Probing Magnetic Fields and Measuring Magnetization
• The Velocity Statistics of Turbulent Clouds in the Presence of Gravity, Magnetic fields, Radiation, and Outflow Feedback
• Cosmic ray streaming in the turbulent interstellar medium
• Decomposing Magnetic Fields in Three Dimensions over the Central Molecular Zone
• Wide binary stars formed in the turbulent interstellar medium