The LOFAR Two-metre Sky Survey: Deep Fields Data Release 2

I. The ELAIS-N1 field

¹ ASTRON, The Netherlands Institute for Radio Astronomy, Postbus 2 NL-7990 AA Dwingeloo, The Netherlands
² Leiden Observatory, Leiden University, PO Box 9513 2300 RA Leiden, The Netherlands
³ Astrophysics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
⁴ Institute for Astronomy, School of Physics and Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
⁵ INAF-Istituto di Radioastronomia, Via P. Gobetti 101, 40129 Bologna, Italy
⁶ Thüringer Landessternwarte, Sternwarte 5, D-07778 Tautenburg, Germany
⁷ Centre for Astrophysics Research, University of Hertfordshire, Hatfield, Herts AL10 9AB, UK
⁸ Ruđer Bošković Institute, Bijenička cesta 54, 10000 Zagreb, Croatia
⁹ GEPI, Observatoire de Paris, Université PSL, CNRS, 5 Place Jules Janssen, 92190 Meudon, France
¹⁰ Department of Physics & Electronics, Rhodes University, PO Box 94 Grahamstown 6140, South Africa
¹¹ SKA Observatory, Jodrell Bank, Lower Withington, Macclesfield SK11 9FT, United Kingdom
¹² DIFA – Università di Bologna, Via P. Gobetti 93, 40129 Bologna, Italy
¹³ Hamburg Observatory, University of Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
¹⁴ Chalmers University of Technology, Onsala Space Observatory, SE-43992, Onsala, Sweden
¹⁵ Anton Pannekoek Institute for Astronomy, University of Amsterdam, Postbus 94249 1090 GE Amsterdam, The Netherlands
¹⁶ National Centre for Nuclear Research, Pasteura 7, 02-093 Warsaw, Poland
¹⁷ Astronomy Department, Universidad de Concepción, Casilla 160-C, Concepción, Chile
¹⁸ Max Planck Institute for Radio Astronomy, Auf dem Hügel 69, 53121 Bonn, Germany
¹⁹ Centre for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
²⁰ Institute for Computational Cosmology, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
²¹ Kapteyn Astronomical Institute, University of Groningen, Landleven 12, 9747 AD Groningen, The Netherlands

^⋆ Corresponding author; shimwell@astron.nl

Received: 8 November 2024
Accepted: 28 December 2024

Abstract

We present the final 6″ resolution data release of the ELAIS-N1 field from the LOw-Frequency ARray (LOFAR) Two-metre Sky Survey Deep Fields project (LoTSS Deep). The 144 MHz images are the most sensitive achieved to date at this frequency and were created from 290 TB of data obtained from 505 h on-source observations taken over 7.5 years. The data were processed following the strategies developed for previous LoTSS and LoTSS Deep data releases. The resulting images span 24.53 square degrees, and using a refined source detection approach, we identified 154 952 radio sources formed from 182 184 Gaussian components within this area. The maps reach a noise level of 10.7 μJy beam⁻¹ at 6″ resolution, where approximately half of the noise is due to source confusion. In about 7.4% of the image, our limited dynamic range around bright sources results in a further > 5% increase in the noise. The images have a flux density scale accuracy of about 9%, and the standard deviation of offsets between our source positions and those from Pan-STARRS is 0.2″ in RA and Dec for high significance detections. We searched individual epoch images for variable sources, identifying 39 objects with considerable variation. We also searched for circularly polarised sources, achieving three detections of previously known emitters (two stars and one pulsar) whilst constraining the typical polarisation fraction plus leakage to be less than 0.045%.