Polarimetry of a Giant Radio Galaxy. A polarization analysis of the Double Irony giant radio galaxy in the 4-8 GHz range

Abstract

Radio galaxies can display jets and lobes of radio emission from an active galactic nucleus located at the center of their host galaxy. These jets and lobes extend well beyond the host galaxy. The radio structures are valuable probes of the environment of the galaxies into which they expand. Polarimetry provides additional information of the magneto-ionic medium in and around radio galaxies. New observational data of synchrotron emission from the Giant Radio Galaxy named Double Irony were imaged and analysed. The radio galaxy extends about 1100 kiloparsec in length and lies at a redshift of 0.138. This observation was made by the Jansky Very Large Array interferometer in the 4.2 to 8.2 GHz frequency range, with a 2 MHz spectral resolution. The Stokes I data were calibrated using a calibration pipeline. Polarimetry data were manually calibrated using the output of the calibration pipeline as a starting point. Wideband Stokes I continuum was first imaged. The resulting images have a higher angular resolution than previous works with a synthesised beam of 3.3600 × 2.6500 , or 8.21 × 6.47 kiloparsec. After primary beam attenuation correction the spectral index map was calculated, using both wideband images and individual frequency bands of 128 MHz. Using Rotation Measure Synthesis, the Stokes Q and Stokes U wideband data were corrected for Rotation Measure. Linear polarisation intensity and linear polarisation angles were obtained, and the magnetic field distribution in the different structures of Double Irony was calculated. The polarimetry data show signs of helical magnetic fields with toroidal magnetic field components around certain parts of the jets.