Faraday rotation at low frequencies: magnetoionic material of the large FRII radio galaxy PKS J0636-2036

TL;DR

This study uses low-frequency broadband polarization observations to analyze the Faraday rotation and depolarization properties of the FRII radio galaxy PKS J0636-2036, revealing complex magnetic structures and estimating intergalactic magnetic fields.

Contribution

It provides the first detailed low-frequency polarization analysis of PKS J0636-2036, employing RM synthesis and broadband modeling to characterize Faraday effects and magnetic fields in the source environment.

Findings

Detection of polarized hotspots across 70-230 MHz

Identification of multiple Faraday components in the southern hotspot

Estimated intergalactic magnetic field strengths between 0.04 and 0.5 μG

Abstract

We present a low-frequency, broadband polarization study of the FRII radio galaxy PKS J0636-2036 (z = 0.0551), using the Murchison Widefield Array (MWA) from 70 to 230 MHz. The northern and southern hotspots (separated by ~14.5' on the sky) are resolved by the MWA (3'.3 resolution) and both are detected in linear polarization across the full frequency range. A combination of Faraday rotation measure (RM) synthesis and broadband polarization model-fitting are used to constrain the Faraday depolarization properties of the source. For the integrated southern hotspot emission, two RM component models are strongly favoured over a single RM component, and the best-fitting model requires Faraday dispersions of approximately 0.7 and 1.2 rad/m$^2$ (with a mean RM of ~50 rad/m$^2$). High resolution imaging at 5" with the ATCA shows significant sub-structure in the southern hotspot and highlights some of the limitations in the polarization modelling of the MWA data. Based on the observed depolarization, combined with extrapolations of gas density scaling-relations for group environments, we estimate magnetic field strengths in the intergalactic medium between ~0.04 and 0.5 {\mu}G. We also comment on future prospects of detecting more polarized sources at low frequencies.