A Wideband Polarization Observation of Hydra A with the Jansky Very Large Array

TL;DR

This study provides a detailed wideband polarization analysis of Hydra A, revealing complex Faraday rotation and depolarization behaviors indicative of turbulent magnetic fields on sub-kiloparsec scales.

Contribution

It offers the first high-resolution, wideband polarization measurements of Hydra A, modeling depolarization with a simple RM screen and revealing turbulence in the Faraday rotating medium.

Findings

Large Faraday rotation measures from -12300 to 5000 rad/m^2.

Depolarization shows non-monotonic, oscillatory behavior with wavelength.

Depolarization explained by magnetic field fluctuations on <1500 pc scales.

Abstract

We present results of a wideband high-resolution polarization study of Hydra A, one of the most luminous FR I radio galaxies known and amongst the most well-studied. The radio emission from this source displays extremely large Faraday rotation measures (RM), ranging from -12300 rad m$^{-2}$ to 5000 rad m$^{-2}$, the majority of which are believed to originate from magnetized thermal gas external to the radio tails. The radio emission from both tails strongly depolarizes with decreasing frequency. The depolarization, as a function of wavelength, is commonly non-monotonic, often showing oscillatory behavior, with strongly non-linear rotation of the polarization position angle with $\lambda^2$. A simple model, based on the RM screen derived from the high frequency, high resolution data, predicts the lower frequency depolarization remarkably well. The success of this model indicates the majority of the depolarization can be attributed to fluctuations in the magnetic field on scales $< 1500$ pc, suggesting the presence of turbulent magnetic field/electron density structures on sub-kpc scales within a Faraday rotating (FR) medium.