Estimation of Magnetic Field Strength in the Turbulent Warm Ionized Medium

TL;DR

This study uses magnetohydrodynamic turbulence simulations to analyze Faraday rotation measures in turbulent warm ionized media, revealing that RM accurately reflects magnetic field strength and that RM distributions are Gaussian with widths indicating field strength.

Contribution

It demonstrates that RM/DM reliably estimates magnetic field strength in turbulent media and characterizes the distribution of RMs in such environments.

Findings

RM/DM accurately estimates magnetic field strength.

RM distributions are Gaussian with widths related to field strength.

No strong correlation between magnetic field fluctuations and gas density.

Abstract

We studied Faraday rotation measure (RM) in turbulent media with the rms Mach number of unity, using isothermal, magnetohydrodynamic turbulence simulations. Four cases with different values of initial plasma beta were considered. Our main findings are as follows. (1) There is no strong correlation between the fluctuations of magnetic field strength and gas density. So the magnetic field strength estimated with RM/DM (DM is the dispersion measure) correctly represents the true mean strength of the magnetic field along the line of sight. (2) The frequency distribution of RMs is well fitted to the Gaussian. In addition, there is a good relation between the width of the distribution of RM/$\bar{\rm RM}$ ($\bar{\rm RM}$ is the average value of RMs) and the strength of the regular field along the line of sight; the width is narrower, if the field strength is stronger. We discussed the implications of our findings in the warm ionized medium where the Mach number of turbulent motions is around unity.