Untangling Cosmic Magnetic Fields: Faraday Tomography at Metre Wavelengths with LOFAR
Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, D-21029 Hamburg, Germany
Dunlap Institute for Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4, Canada
Centre for Astrophysics Research, School of Physics, Astronomy and Mathematics, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
Department of Astrophysics/IMAPP, Radboud University Nijmegen, P.O. Box 9010, 6500 GL Nijmegen, The Netherlands
ASTRON, The Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands
GEPI & USN, Observatoire de Paris, Université PSL, CNRS, 5 Place Jules Janssen, 92190 Meudon, France
INAF—Osservatorio Astronomico di Cagliari, Via della Scienza 5, 09047 Selargius (CA), Italy
Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 43992 Onsala, Sweden
CSIRO Astronomy and Space Science, P.O. Box 1130, Bentley 6102, Australia
Author to whom correspondence should be addressed.
Received: 26 October 2018 / Revised: 16 November 2018 / Accepted: 19 November 2018 / Published: 29 November 2018
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 centimetre-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 (Active Galactic Nucleus). 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
(with ∼13% of all sources having a linear size >1 Mpc). 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 eight blazars. Most sources display simple Faraday spectra, but we highlight one blazar that displays a complex Faraday spectrum, with two close peaks in the Faraday dispersion function.
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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 SP, Brüggen M, Van Eck CL, Hardcastle MJ, Haverkorn M, Shimwell TW, Tasse C, Vacca V, Horellou C, Heald G. Untangling Cosmic Magnetic Fields: Faraday Tomography at Metre Wavelengths with LOFAR. Galaxies. 2018; 6(4):126.
O’Sullivan, Shane P.; Brüggen, Marcus; Van Eck, Cameron L.; Hardcastle, Martin J.; Haverkorn, Marijke; Shimwell, Timothy W.; Tasse, Cyril; Vacca, Valentina; Horellou, Cathy; Heald, George. 2018. "Untangling Cosmic Magnetic Fields: Faraday Tomography at Metre Wavelengths with LOFAR." Galaxies 6, no. 4: 126.
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