Magnetic Field and Faraday Rotation Measure in the Turbulent Warm Ionized Medium

Abstract

Wu et al. (2009) suggested an empirical relation between the magnetic field strength along the line of sight (LOS) and the dispersion of Faraday rotation measure (RM) distribution in turbulent media with root-mean-square sonic Mach number $M_s\simeq 1$. In this paper, we extend the work by incorporating the Mach number dependence. Media with $\sim 0.5<M_s<\sim 2$ are considered to cover the Mach number range of the warm ionized medium (WIM) of our Galaxy. Three-dimensional, magnetohydrodynamic isothermal turbulence simulations with solenoidal forcing are used. We suggest a new relation among the LOS magnetic field strength, the dispersion of RM distribution, and the Mach number, which approximately represents the relation for Alfvénic perturbations. In addition, we suggest a relation between the Mach number and the dispersion of log-normal distribution of emission measure (EM), which is basically the relation for the Mach number and the density dispersion. The relations could be used for a quick and rough estimation of the LOS magnetic field strength in the turbulent WIM.

To appear in New Astronomy

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• As a matter of force - Systematic biases in idealized turbulence simulations
• Features of collisionless turbulence in the intracluster medium from simulated Faraday Rotation maps
• Intermittent fragmentation and statistical variations during gas collapse in magnetised atomic cooling haloes
• Peering into the Milky Way by FAST: III. Magnetic fields in the Galactic halo and farther spiral arms revealed by the Faraday effect of faint pulsars
• The Galactic Faraday rotation sky 2020