The LOFAR Two-metre Sky Survey

I. Survey description and preliminary data release^⋆

¹ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
² SUPA, Institute for Astronomy, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ, UK
³ Centre for Astrophysics Research, School of Physics, Astronomy and Mathematics, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
⁴ ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands
⁵ CSIRO Astronomy and Space Science, 26 Dick Perry Avenue, Kensington 6151 WA, Australia
⁶ Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen, The Netherlands
⁷ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁸ Sydney Institute for Astronomy, School of Physics A28, The University of Sydney, NSW 2006, Australia
⁹ ARC Centre of Excellence for All-Sky Astrophysics (CAASTRO), Australia
¹⁰ University of Hamburg, Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
¹¹ GEPI, Observatoire de Paris, CNRS, Universite Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France
¹² Department of Physics & Electronics, Rhodes University, PO Box 94, Grahamstown, 6140, South Africa
¹³ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
¹⁴ INAF–Istituto di Radioastronomia, via Gobetti 101, 40129 Bologna, Italy
¹⁵ Astronomical Observatory, Jagiellonian University, ul. Orla 171, 30-244 Kraków, Poland
¹⁶ Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
¹⁷ Department of Astrophysics/IMAPP, Radboud University Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands
¹⁸ Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester Manchester M13 9PL UK
¹⁹ Astrophysics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford, OX1 3RH, UK
²⁰ Physics and Astronomy Department, University of the Western Cape, 7535 Bellville, South Africa
²¹ Department of Physics and Astronomy, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
²² RAL Space, The Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0NL, UK
²³ Astronomical Institute “Anton Pannekoek”, University of Amsterdam, Postbus 94249, 1090 GE Amsterdam, The Netherlands
²⁴ Joint Institute for VLBI in Europe, Postbus 2, 7990 AA Dwingeloo, The Netherlands
²⁵ Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany
²⁶ Station de Radioastronomie de Nançay, Observatoire de Paris, CNRS/INSU USR 704, Université d’Orléans OSUC, route de Souesmes, 18330 Nançay, France
²⁷ Laboratoire Lagrange, Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Bvd de l’Observatoire, CS 34229, 06304 Nice Cedex 4, France
²⁸ Astronomisches Institut Ruhr-Universität Bochum/Forschungszentrum Jülich, JSC, 52425 Jülich, Germany
²⁹ School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, UK
³⁰ International Centre for Radio Astronomy Research (ICRAR), The University of Western Australia, 35 Stirling Hwy, Crawley WA 6009, Australia
³¹ Institute of Cosmology & Gravitation, University of Portsmouth, Burnaby Road, PO1 3FX, Portsmouth, UK
³² Toruń Centre for Astronomy, Faculty of Physics, Astronomy and Informatics, NCU, Grudziacka 5, 87-100 Toruń, Poland
³³ Sodankylä Geophysical Observatory, University of Oulu, Tähteläntie 62, 99600 Sodankylä, Finland
³⁴ STFC Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Didcot OX11 0QX, UK
³⁵ National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, 411007 Pune, India
³⁶ Fakultät für Physik, Universität Bielefeld, Postfach 100131, 33501 Bielefeld, Germany
³⁷ Leibniz Institute for Astrophysics Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
³⁸ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
³⁹ Department of Astronomy, University of Cape Town, 7701 Rondebosch, South Africa

^⋆⋆ Corresponding author: T. W. Shimwell, e-mail: shimwell@strw.leidenuniv.nl

Received: 14 July 2016
Accepted: 7 November 2016

Abstract

The LOFAR Two-metre Sky Survey (LoTSS) is a deep 120–168 MHz imaging survey that will eventually cover the entire northern sky. Each of the 3170 pointings will be observed for 8 h, which, at most declinations, is sufficient to produce ~5″ resolution images with a sensitivity of ~100 μJy/beam and accomplish the main scientific aims of the survey, which are to explore the formation and evolution of massive black holes, galaxies, clusters of galaxies and large-scale structure. Owing to the compact core and long baselines of LOFAR, the images provide excellent sensitivity to both highly extended and compact emission. For legacy value, the data are archived at high spectral and time resolution to facilitate subarcsecond imaging and spectral line studies. In this paper we provide an overview of the LoTSS. We outline the survey strategy, the observational status, the current calibration techniques, a preliminary data release, and the anticipated scientific impact. The preliminary images that we have released were created using a fully automated but direction-independent calibration strategy and are significantly more sensitive than those produced by any existing large-area low-frequency survey. In excess of 44 000 sources are detected in the images that have a resolution of 25″, typical noise levels of less than 0.5 mJy/beam, and cover an area of over 350 square degrees in the region of the HETDEX Spring Field (right ascension 10h45m00s to 15h30m00s and declination 45°00′00″ to 57°00′00″).