Broad-band radio polarimetry of disc galaxies and AGN with KAT-7

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.