@article{1a76e8aa8fe94e4fb668ad30cbcf9b9f,
title = "The LOFAR Two Meter Sky Survey: Deep Fields Data Release 1: I. Direction-dependent calibration and imaging",
abstract = "The Low Frequency Array (LOFAR) is an ideal instrument to conduct deep extragalactic surveys. It has a large field of view and is sensitive to large-scale and compact emission. It is, however, very challenging to synthesize thermal noise limited maps at full resolution, mainly because of the complexity of the low-frequency sky and the direction dependent effects (phased array beams and ionosphere). In this first paper of a series, we present a new calibration and imaging pipeline that aims at producing high fidelity, high dynamic range images with LOFAR High Band Antenna data, while being computationally efficient and robust against the absorption of unmodeled radio emission. We apply this calibration and imaging strategy to synthesize deep images of the Bo{\"o}tes and Lockman Hole fields at ~150 MHz, totaling ~80 and ~100 h of integration, respectively, and reaching unprecedented noise levels at these low frequencies of {\^a} 30 and {\^a} 23 μJy beam-1 in the inner ~3 deg2. This approach is also being used to reduce the{\^a}» LOTSS-wide data for the second data release.",
keywords = "Galaxies: Active, Galaxies: starburst, Radio continuum: galaxies, Surveys, Techniques: image processing, Techniques: interferometric",
author = "C. Tasse and T. Shimwell and Hardcastle, {M. J.} and O'Sullivan, {S. P.} and {van Weeren}, R. and Best, {P. N.} and L. Bester and B. Hugo and O. Smirnov and J. Sabater and G. Calistro-Rivera and {de Gasperin}, F. and Morabito, {L. K.} and H. R{\"o}ttgering and Williams, {W. L.} and M. Bonato and M. Bondi and A. Botteon and M. Br{\"u}ggen and G. Brunetti and Chyay, {K. T.} and Garrett, {M. A.} and G. G{\"u}rkan and Jarvis, {M. J.} and R. Kondapally and S. Mandal and I. Prandoni and A. Repetti and E. Retana-Montenegro and Schwarz, {D. J.} and A. Shulevski and Y. Wiaux",
note = "Funding Information: Acknowledgements. This paper is based (in part) on data obtained with the International LOFAR Telescope (ILT). LOFAR (van Haarlem et al. 2013) is the Low Frequency Array designed and constructed by ASTRON. It has observing, data processing, and data storage facilities in several countries, which are owned by various parties (each with their own funding sources), and which are collectively operated by the ILT foundation under a joint scientific policy. The ILT resources have benefitted from the following recent major funding sources: CNRS-INSU, Observatoire de Paris and Universit{\'e} d{\textquoteright}Orl{\'e}ans, France; BMBF, MIWF-NRW, MPG, Germany; Science Foundation Ireland (SFI), Department of Business, Enterprise and Innovation (DBEI), Ireland; NWO, The Netherlands; The Science and Technology Facilities Council, UK; Ministry of Science and Higher Education, Poland. This work makes use of kern astronomical software package (available at https://kernsuite.info and presented in Molenaar & Smirnov 2018). M.B. acknowledges support from INAF under PRIN SKA/CTA FORECaST. M.B. acknowledges the support from the Minis-tero degli Affari Esteri della Cooperazione Internazionale – Direzione Generale per la Promozione del Sistema Paese Progetto di Grande Rilevanza ZA18GR02. M.J.J. acknowledges support from the UK Science and Technology Facilities Council [ST/N000919/1] and the Oxford Hintze Centre for Astrophysical Surveys which is funded through generous support from the Hintze Family Charitable Foundation. P.N.B. and J.S. are grateful for support from the UK STFC via grant ST/R000972/1. M.J.H. acknowledges support from STFC via grant ST/R000905/1. W.L.W. acknowledges support from the ERC Advanced Investigator programme NewClusters 321271. W.L.W. also acknowledges support from the CAS-NWO programme for radio astronomy with project number 629.001.024, which is financed by the Netherlands Organisation for Scientific Research (NWO). A.B. acknowledges support from the VIDI research programme with project number 639.042.729, which is financed by the Netherlands Organisation for Scientific Research (NWO). I.P. acknowledges support from INAF under the SKA/CTA PRIN “FORECaST” and the PRIN MAIN STREAM “SAuROS” projects M.B. acknowledges support from INAF under PRIN SKA/CTA FORECaST and from the Ministero degli Affari Esteri della Cooperazione Internazionale - Direzione Generale per la Promozione del Sis-tema Paese Progetto di Grande Rilevanza ZA18GR02. R.K. acknowledges support from the Science and Technology Facilities Council (STFC) through an STFC studentship. Publisher Copyright: {\textcopyright} C. Tasse et al. 2021. Copyright: Copyright 2021 Elsevier B.V., All rights reserved.",
year = "2021",
month = apr,
doi = "10.1051/0004-6361/202038804",
language = "English",
volume = "648",
journal = "Astronomy and Astrophysics",
issn = "0004-6361",
publisher = "EDP Sciences",
}