Volume 622, February 2019
LOFAR Surveys: a new window on the Universe
|Number of page(s)||17|
|Published online||19 February 2019|
The LOFAR Two-metre Sky Survey
IV. First Data Release: Photometric redshifts and rest-frame magnitudes⋆,⋆⋆
Leiden Observatory, Leiden University, PO Box 9513
Leiden, The Netherlands
2 SUPA, Institute for Astronomy, Royal Observatory, Blackford Hill, EH9 3HJ Edinburgh, UK
3 Astrophysics, University of Oxford, Denys Wilkinson Building, Keble Road, OX1 3RH Oxford, UK
4 Centre for Astrophysics Research, School of Physics, Astronomy and Mathematics, University of Hertfordshire, College Lane, AL10 9AB Hatfield, UK
5 ASTRON, The Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands
6 School of Physical Sciences, The Open University, Walton Hall, MK7 6AA Milton Keynes, UK
7 INAF – Istituto di Radioastronomia, via Gobetti 101, 40129 Bologna, Italy
8 GEPI, Observatoire de Paris, CNRS, Université Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France
9 Space Science & Technology Department, The Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0NL Oxfordshire, UK
10 Astronomical Observatory, Jagiellonian University, ul. Orla 171, 30-244 Kraków, Poland
11 CSIRO Astronomy and Space Science, PO Box 1130, 6102 Bentley, WA, Australia
12 Thüringer Landessternwarte (TLS), Sternwarte 5, 07778 Tautenburg, Germany
13 Fakultät für Physik, Universität Bielefeld, Postfach 100131, 33501 Bielefeld, Germany
Accepted: 6 August 2018
The LOFAR Two-metre Sky Survey (LoTSS) is a sensitive, high-resolution 120–168 MHz survey of the Northern sky. The LoTSS First Data Release (DR1) presents 424 square degrees of radio continuum observations over the HETDEX Spring Field (10h45m00s < right ascension < 15h30m00s and 45°00′00″ < declination < 57°00′00″) with a median sensitivity of 71 μJy beam−1 and a resolution of 6″. In this paper we present photometric redshifts (photo-z) for 94.4% of optical sources over this region that are detected in the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) 3π steradian survey. Combining the Pan-STARRS optical data with mid-infrared photometry from the Wide-field Infrared Survey Explorer, we estimate photo-zs using a novel hybrid photometric redshift methodology optimised to produce the best possible performance for the diverse sample of radio continuum selected sources. For the radio-continuum detected population, we find an overall scatter in the photo-z of 3.9% and an outlier fraction (|zphot−zspec|/(1 + zspec) > 0.15) of 7.9%. We also find that, at a given redshift, there is no strong trend in photo-z quality as a function of radio luminosity. However there are strong trends as a function of redshift for a given radio luminosity, a result of selection effects in the spectroscopic sample and/or intrinsic evolution within the radio source population. Additionally, for the sample of sources in the LoTSS First Data Release with optical counterparts, we present rest-frame optical and mid-infrared magnitudes based on template fits to the consensus photometric (or spectroscopic when available) redshift.
Key words: radio continuum: galaxies / galaxies: active / galaxies: distances and redshifts
The catalogue is available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (18.104.22.168) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/622/A1
© ESO 2019
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