The LOFAR Two-metre Sky Survey - II. First data release
Creators: name: Shimwell, T. W.
name: Tasse, C.
name: Hardcastle, M. J.
name: Mechev, A. P.
name: Williams, W. L.
name: Best, P. N.
name: Röttgering, H. J. A.
name: Callingham, J. R.
name: Dijkema, T. J.
name: de Gasperin, F.
name: Hoang, D. N.
name: Hugo, B.
name: Mirmont, M.
name: Oonk, J. B. R.
name: Prandoni, I.
name: Rafferty, D.
name: Sabater, J.
name: Smirnov, O.
name: van Weeren, R. J.
name: White, G. J.
name: Atemkeng, M.
name: Bester, L.
name: Bonnassieux, E.
name: Brüggen, M.
name: Brunetti, G.
name: Chyży, K. T.
name: Cochrane, R.
name: Conway, J. E.
name: Croston, J. H.
name: Danezi, A.
name: Duncan, K.
name: Haverkorn, M.
name: Heald, G. H.
name: Iacobelli, M.
name: Intema, H. T.
name: Jackson, N.
name: Jamrozy, M.
name: Jarvis, M. J.
name: Lakhoo, R.
name: Mevius, M.
name: Miley, G. K.
name: Morabito, L.
name: Morganti, R.
name: Nisbet, D.
name: Orrú, E.
name: Perkins, S.
name: Pizzo, R. F.
name: Schrijvers, C.
name: Smith, D. J. B.
name: Vermeulen, R.
name: Wise, M. W.
name: Alegre, L.
name: Bacon, D. J.
name: van Bemmel, I. M.
name: Beswick, R. J.
name: Bonafede, A.
name: Botteon, A.
name: Bourke, S.
name: Brienza, M.
name: Rivera, G. Calistro
name: Cassano, R.
name: Clarke, A. O.
name: Conselice, C. J.
name: Dettmar, R. J.
name: Drabent, A.
name: Dumba, C.
name: Emig, K. L.
name: Enßlin, T. A.
name: Ferrari, C.
name: Garrett, M. A.
name: Génova-Santos, R. T.
name: Goyal, A.
name: Gürkan, G.
name: Hale, C.
name: Harwood, J. J.
name: Heesen, V.
name: Hoeft, M.
name: Horellou, C.
name: Jackson, C.
name: Kokotanekov, G.
name: Kondapally, R.
name: Kunert-Bajraszewska, M.
name: Mahatma, V.
name: Mahony, E. K.
name: Mandal, S.
name: McKean, J. P.
name: Merloni, A.
name: Mingo, B.
name: Miskolczi, A.
name: Mooney, S.
name: Nikiel-Wroczyński, B.
name: O'Sullivan, S. P.
name: Quinn, J.
name: Reich, W.
name: Roskowiński, C.
name: Rowlinson, A.
name: Savini, F.
name: Saxena, A.
name: Schwarz, D. J.
name: Shulevski, A.
name: Sridhar, S. S.
name: Stacey, H. R.
name: Urquhart, S.
name: van der Wiel, M. H. D.
name: Varenius, E.
name: Webster, B.
name: Wilber, A.
Publisher: name: arXiv
Year: 2018
Subjects: subject: Astrophysics of Galaxies (astro-ph.GA)
subject: Cosmology and Nongalactic Astrophysics (astro-ph.CO)
subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: Instrumentation and Methods for Astrophysics (astro-ph.IM)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: The LOFAR Two-metre Sky Survey (LoTSS) is an ongoing sensitive, high-resolution 120-168MHz survey of the entire northern sky for which observations are now 20% complete. We present our first full-quality public data release. For this data release 424 square degrees, or 2% of the eventual coverage, in the region of the HETDEX Spring Field (right ascension 10h45m00s to 15h30m00s and declination 45$^\circ$00$'$00$''$ to 57$^\circ$00$'$00$''$) were mapped using a fully automated direction-dependent calibration and imaging pipeline that we developed. A total of 325,694 sources are detected with a signal of at least five times the noise, and the source density is a factor of $\sim 10$ higher than the most sensitive existing very wide-area radio-continuum surveys. The median sensitivity is S$_{\rm 144 MHz} = 71\,μ$Jy beam$^{-1}$ and the point-source completeness is 90% at an integrated flux density of 0.45mJy. The resolution of the images is 6$''$ and the positional accuracy is within 0.2$''$. This data release consists of a catalogue containing location, flux, and shape estimates together with 58 mosaic images that cover the catalogued area. In this paper we provide an overview of the data release with a focus on the processing of the LOFAR data and the characteristics of the resulting images. In two accompanying papers we provide the radio source associations and deblending and, where possible, the optical identifications of the radio sources together with the photometric redshifts and properties of the host galaxies. These data release papers are published together with a further $\sim$20 articles that highlight the scientific potential of LoTSS.
description: 16 figures, 1 table and 22 pages. This paper is part of the LOFAR surveys data release 1 and has been accepted for publication in a special edition of A&amp;A that will appear in Feb 2019, volume 622. The catalogues and images from the data release will be publicly available on lofar-surveys.org upon publication of the journal