Broad-band Radio Polarimetry of disk galaxies and AGN with KAT 7

TL;DR

This study uses broad-band radio polarimetry with KAT 7 to analyze the Faraday complexity of disk galaxies and AGN, revealing diverse Faraday spectra and polarization properties that inform magnetic field structures.

Contribution

It provides the first broad-band polarization analysis of these sources with KAT 7, demonstrating the utility of Rotation Measure Synthesis in characterizing Faraday complexity.

Findings

AGN sources exhibit simple and complex Faraday spectra.

Some sources show time-variable Faraday spectra.

Disk galaxies display complex Faraday behavior, likely due to turbulence.

Abstract

We report broad-band (1.2 - 1.9 GHz) radio continuum observations at arcminute resolutions of two nearby disk galaxies, NGC 1808 and NGC 1097, and four AGN powered radio sources; PKS B1934-638, PKS B0407-658, J0240-231, and J0538-440. We use Rotation Measure Synthesis to analyze their Faraday complexity. Observations were made with the KAT\,7 radio telescope array, in South Africa. The AGN powered sources fall into two "Faraday" categories -- simple and complex. The most polarized sources, J0538-440 and J0240-231, are found to have complex Faraday spectra that can be time variable (J0538-440 case) and also indicative of complex Faraday emitting and rotating components along the line of sight. PKS B0407-658 shows a simple Faraday spectrum while PKS B1934-638 is undetected in polarization. The disk galaxies are classified as complex, albeit at low signal-to-noise. This may indicate depolarization due to turbulence of the magnetised plasma in the bar and circumnuclear regions and/or frequency-dependent depolarization at L-band