O’Sullivan, S.P.; Brüggen, M.; Van Eck, C.L.; Hardcastle, M.J.; Haverkorn, M.; Shimwell, T.W.; Tasse, C.; Vacca, V.; Horellou, C.; Heald, G. Untangling Cosmic Magnetic Fields: Faraday Tomography at Metre Wavelengths with LOFAR. Galaxies2018, 6, 126.
O’Sullivan, S.P.; Brüggen, M.; Van Eck, C.L.; Hardcastle, M.J.; Haverkorn, M.; Shimwell, T.W.; Tasse, C.; Vacca, V.; Horellou, C.; Heald, G. Untangling Cosmic Magnetic Fields: Faraday Tomography at Metre Wavelengths with LOFAR. Galaxies 2018, 6, 126.
O’Sullivan, S.P.; Brüggen, M.; Van Eck, C.L.; Hardcastle, M.J.; Haverkorn, M.; Shimwell, T.W.; Tasse, C.; Vacca, V.; Horellou, C.; Heald, G. Untangling Cosmic Magnetic Fields: Faraday Tomography at Metre Wavelengths with LOFAR. Galaxies2018, 6, 126.
O’Sullivan, S.P.; Brüggen, M.; Van Eck, C.L.; Hardcastle, M.J.; Haverkorn, M.; Shimwell, T.W.; Tasse, C.; Vacca, V.; Horellou, C.; Heald, G. Untangling Cosmic Magnetic Fields: Faraday Tomography at Metre Wavelengths with LOFAR. Galaxies 2018, 6, 126.
Abstract
The technique of Faraday tomography is a key tool for the study of magnetised plasmas in the new era of broadband radio polarisation observations. In particular, observations at metre-wavelengths provide significantly better Faraday depth accuracies compared to traditional cm-wavelength observations. However, the effect of Faraday depolarisation makes the polarised signal very challenging to detect at metre wavelengths (MHz frequencies). In this work, Faraday tomography is used to characterise the Faraday rotation properties of polarised sources found in data from the LOFAR Two-Metre Sky Survey (LoTSS). Of the 76 extragalactic polarised sources analysed here, we find that all host a radio-loud AGN. The majority of the sources (∼64%) are large FRII radio galaxies with a median projected linear size of 710 kpc and median radio luminosity at 144 MHz of 4 × 10^26 W/Hz. In several cases, both hotspots are detected in polarisation at an angular resolution of ∼20". One such case allowed a study of intergalactic magnetic fields on scales of 3.4 Mpc. Other detected source types include an FRI radio galaxy and at least 8 blazars. Most sources display simple Faraday spectra, however, we highlight one blazar that displays a complex Faraday spectrum, with two close peaks in the Faraday dispersion function.
Keywords
magnetic fields; Faraday tomography; large-scale structure; AGN; Milky Way
Subject
Physical Sciences, Astronomy and Astrophysics
Copyright:
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.