University of Hertfordshire

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From the same journal

By the same authors

The LOFAR Two-metre Sky Survey: Deep Fields. II. The ELAIS-N1 LOFAR deep field

Research output: Contribution to journalArticlepeer-review


  • J. Sabater
  • P. N. Best
  • C. Tasse
  • T. W. Shimwell
  • D. Nisbet
  • V. Jelic
  • J. R. Callingham
  • H. J. A. Rottgering
  • M. Bonato
  • M. Bondi
  • B. Ciardi
  • R. K. Cochrane
  • M. J. Jarvis
  • R. Kondapally
  • L. V. E. Koopmans
  • S. P. O'Sullivan
  • I. Prandoni
  • D. J. Schwarz
  • L. Wang
  • W. L. Williams
  • S. Zaroubi
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Original languageEnglish
JournalAstronomy & Astrophysics
Publication statusAccepted/In press - 31 Jul 2020


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 ~10 microJy/bm over 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 hours, it reaches a root mean square (RMS) noise level below 20 microJy/bm in the central region (and below 30 microJy/bm over 10 square degrees). The resolution is 6 arcsecs and 84862 radio sources were detected in the full area (68 sq. deg.) with 74127 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 sq. deg. in the central ~5 sq. deg. region. We present the calibration procedure, which addresses the special configuration of some observations and the extended bandwidth covered (115 to 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%. 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% for ELAIS-N1.


© 2020 ESO

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