The LOFAR Two-meter Sky Survey: Deep Fields Data Release 1
Astronomy and Astrophysics, vol. 648, pp. A2
Abstract
The LOFAR Two-metre Sky Survey (LoTSS) will cover the full northern sky and, additionally, aims to observe the LoTSS deep fields to a noise level of ≲10μJy beam−1over several tens of square degrees in areas that have the most extensive ancillary data. This paper presents the ELAIS-N1 deep field, the deepest of the LoTSS deep fields to date. With an effective observing time of 163.7 h, it reaches a root mean square noise level of ≲20μJy beam−1in the central region (and below 30μJy beam−1over 10 square degrees). The resolution is ~6 arcsecs and 84 862 radio sources were detected in the full area (68 square degrees) with 74 127 sources in the highest quality area at less than 3 degrees from the pointing centre. The observation reaches a sky density of more than 5000 sources per square degree in the central region (~5 square degrees). We present the calibration procedure, which addresses the special configuration of some observations and the extended bandwidth covered (115–177 MHz; central frequency 146.2 MHz) compared to standard LoTSS. We also describe the methods used to calibrate the flux density scale using cross-matching with sources detected by other radio surveys in the literature. We find the flux density uncertainty related to the flux density scale to be ~6.5 per cent. By studying the variations of the flux density measurements between different epochs, we show that relative flux density calibration is reliable out to about a 3 degree radius, but that additional flux density uncertainty is present for all sources at about the 3 per cent level; this is likely to be associated with residual calibration errors, and is shown to be more significant in datasets with poorer ionosphere conditions. We also provide intra-band spectral indices, which can be useful to detect sources with unusual spectral properties. The final uncertainty in the flux densities is estimated to be ~10 per cent for ELAIS-N1.
Authors 22
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Royal Observatory · UK Astronomy Technology Centre
Affiliation as printed
SUPA, Institute for Astronomy, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ, UK
UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ, UK
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Affiliation as printed
SUPA, Institute for Astronomy, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ, UK
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Centre National de la Recherche Scientifique · Rhodes University · Observatoire de Paris · Galaxies, Etoiles, Physique et Instrumentation · Université Paris Diderot
Affiliation as printed
Department of Physics & Electronics, Rhodes University, PO Box 94, Grahamstown, 6140, South Africa
GEPI, Observatoire de Paris, CNRS, Universite Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France
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Affiliation as printed
Centre for Astrophysics Research, School of Physics, Astronomy and Mathematics, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
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Netherlands Institute for Radio Astronomy
Affiliation as printed
ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands
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Affiliation as printed
Ruđer Bošković Institute, Bijenička cesta 54, 10 000 Zagreb, Croatia
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Leiden University · Leiden Observatory · Netherlands Institute for Radio Astronomy
Affiliation as printed
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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Leiden University · Leiden Observatory
Affiliation as printed
Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
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Istituto di Radioastronomia di Bologna · Osservatorio Astronomico di Padova · National Institute for Astrophysics
Affiliation as printed
INAF – Istituto di Radioastronomia, via Gobetti 101, 40129 Bologna, Italy
INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
Italian ALMA Regional Centre, Via Gobetti 101, 40129 Bologna, Italy
INAF – Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy
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Istituto di Radioastronomia di Bologna
Affiliation as printed
INAF – Istituto di Radioastronomia, via Gobetti 101, 40129 Bologna, Italy
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Max Planck Institute for Astrophysics
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Max Planck Institute for Astrophysics, Karl-Schwarzschild-Str. 1, 85748 Garching, Germany
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Center for Astrophysics Harvard & Smithsonian
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Harvard-Smithsonian Center for Astrophysics, 60 Garden St, Cambridge, MA 02138, USA
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University of Oxford · University of the Western Cape
Affiliation as printed
Astrophysics, Department of Physics, Keble Road, OX1 3RH, UK
University of the Western Cape, Private Bag X17, Bellville, Cape Town 7535, South Africa
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Affiliation as printed
SUPA, Institute for Astronomy, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ, UK
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Affiliation as printed
Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen, The Netherlands
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Affiliation as printed
School of Physical Sciences and Centre for Astrophysics & Relativity, Dublin City University, Glasnevin, D09 W6Y4, Ireland
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Istituto di Radioastronomia di Bologna
Affiliation as printed
INAF – Istituto di Radioastronomia, via Gobetti 101, 40129 Bologna, Italy
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Affiliation as printed
Fakultät für Physik, Universität Bielefeld, Postfach 100131, 33501 Bielefeld, Germany
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Affiliation as printed
Centre for Astrophysics Research, School of Physics, Astronomy and Mathematics, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
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University of Groningen · Space Research Organisation Netherlands
Affiliation as printed
Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen, The Netherlands
SRON Netherlands Institute for Space Research, Landleven 12 9747 AD, Groningen, 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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Affiliation as printed
Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen, The Netherlands
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