The LOFAR Two-Metre Sky Survey
Astronomy and Astrophysics, vol. 678, pp. A151
Abstract
The second data release of the LOFAR Two-Metre Sky Survey (LoTSS) covers 27% of the northern sky, with a total area of ~5700 deg 1 . The high angular resolution of LOFAR with Dutch baselines (6 arcsec) allows us to carry out optical identifications of a large fraction of the detected radio sources without further radio followup; however, the process is made more challenging by the many extended radio sources found in LOFAR images as a result of its excellent sensitivity to extended structure. In this paper we present source associations and identifications for sources in the second data release based on optical and near-infrared data, using a combination of a likelihood-ratio cross-match method developed for our first data release, our citizen science project Radio Galaxy Zoo: LOFAR, and new approaches to algorithmic optical identification, together with extensive visual inspection by astronomers. We also present spectroscopic or photometric redshifts for a large fraction of the optical identifications. In total 4 116 934 radio sources lie in the area with good optical data, of which 85% have an optical or infrared identification and 58% have a good redshift estimate. We demonstrate the quality of the dataset by comparing it with earlier optically identified radio surveys. This is by far the largest ever optically identified radio catalogue, and will permit robust statistical studies of star-forming and radio-loud active galaxies.
Authors 48
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Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
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SKA Observatory, Jodrell Bank, Lower Withington, Macclesfield SK11 9FT, UK
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Royal Observatory · University of Edinburgh
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Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
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Royal Observatory · University of Edinburgh
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Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
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School of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK
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School of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK
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School of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK
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Leiden University · Leiden Observatory
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Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
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Leiden University · Leiden Observatory
Affiliation as printed
Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
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Royal Observatory · University of Edinburgh
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Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
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Netherlands Institute for Radio Astronomy
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ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands
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Affiliation as printed
Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
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Royal Observatory · University of Edinburgh
Affiliation as printed
Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
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Istituto di Radioastronomia di Bologna · National Institute for Astrophysics
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INAF-Istituto di Radioastronomia, Via P. Gobetti 101, 40129 Bologna, Italy
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Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029, Hamburg, Germany
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Thüringer Landessternwarte Tautenburg
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Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany
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Universität Hamburg · Istituto di Radioastronomia di Bologna · National Institute for Astrophysics
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Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029, Hamburg, Germany
INAF-Istituto di Radioastronomia, Via P. Gobetti 101, 40129 Bologna, Italy
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Commonwealth Scientific and Industrial Research Organisation · University of Hertfordshire · Thüringer Landessternwarte Tautenburg
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CSIRO Space and Astronomy, ATNF, PO Box 1130, Bentley, WA 6102, Australia
Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany
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University of Warmia and Mazury in Olsztyn
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Space Radio-Diagnostics Research Centre, University of Warmia and Mazury, ul.Oczapowskiego 2, 10-719 Olsztyn, Poland
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Royal Observatory · University of Edinburgh
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Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
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Thüringer Landessternwarte Tautenburg
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Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany
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Astronomical Observatory of the Jagiellonian University, ul. Orla 171, 30-244 Krakow, Poland
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Nicolaus Copernicus University
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Institute of Astronomy, Faculty of Physics, Astronomy and Informatics, NCU, Grudziadzka 5, 87-100 Toruń, Poland
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Royal Observatory · University of Edinburgh
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Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
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National Institute for Astrophysics
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INAF-IAPS, Via Fosso del Cavaliere 100, 00133 Rome, Italy
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Thüringer Landessternwarte Tautenburg
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Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany
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Leiden University · Leiden Observatory · Netherlands Institute for Radio Astronomy
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ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands
Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
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Universidad Complutense de Madrid
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Departamento de Fisica de la Tierra y Astrofisica, Universidad Complutense de Madrid, 28040 Madrid, Spain
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Affiliation as printed
Astronomical Observatory of the Jagiellonian University, ul. Orla 171, 30-244 Krakow, Poland
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Affiliation as printed
Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
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Istituto di Radioastronomia di Bologna · National Institute for Astrophysics
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INAF-Istituto di Radioastronomia, Via P. Gobetti 101, 40129 Bologna, Italy
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Fakultät für Physik, Universität Bielefeld, Postfach 100131, 33501 Bielefeld, Germany
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Netherlands Institute for Radio Astronomy
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ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands
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Fakultät für Physik, Universität Bielefeld, Postfach 100131, 33501 Bielefeld, Germany
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Department of Physics, Lancaster University, Lancaster LA1 4YB, UK
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Department of Astronomy, Tsinghua University, Beijing 100084, PR China
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University of Cape Town · Istituto di Radioastronomia di Bologna · Inter-university Institute for Data Intensive Astronomy · University of the Western Cape · National Institute for Astrophysics
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INAF-Istituto di Radioastronomia, Via P. Gobetti 101, 40129 Bologna, Italy
Inter-University Institute for Data Intensive Astronomy, Department of Astronomy, University of Cape Town, 7701 Rondebosch, Cape Town, South Africa
Inter-University Institute for Data Intensive Astronomy, Department of Physics and Astronomy, University of the Western Cape, 7535 Bellville, Cape Town, South Africa
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Leiden University · Chinese Academy of Sciences · Shanghai Astronomical Observatory · Leiden Observatory
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Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, PR China
Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
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Citizen scientist
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Netherlands Institute for Radio Astronomy
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ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands
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Citizen scientist
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Citizen scientist
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Citizen scientist
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Citizen scientist
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Citizen scientist
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Citizen scientist
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Citizen scientist
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Universidad Nacional Autónoma de México
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Universidad Nacional Autonoma de Mexico (UNAM), Avenida Insurgentes Sur 3000, Mexico City, Mexico
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