@article{67f9be61f5744c72a27808eb5129ccf5,
title = "The LOFAR Two-meter Sky Survey: Deep Fields Data Release 1: II. The ELAIS-N1 LOFAR deep field",
abstract = "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 μJy beam−1 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 h, it reaches a root mean square noise level of ≲20 μJy beam−1 in the central region (and below 30 μJy beam−1 over 10 square degrees). The resolution is ~6 arcsecs and 84 862 radio sources were detected in the full area (68 square degrees) with 74 127 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 square degree in the central region (~5 square degrees). We present the calibration procedure, which addresses the special configuration of some observations and the extended bandwidth covered (115-177 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 per cent. 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 per cent for ELAIS-N1. Catalogs and images are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/648/A2 The data associated with this article are released at: https://lofar-surveys.org",
keywords = "surveys, catalogs, radio continuum: general, radio continuum: galaxies, Astrophysics - Astrophysics of Galaxies, Astrophysics - High Energy Astrophysical Phenomena",
author = "J. Sabater and Best, {P. N.} and C. Tasse and Hardcastle, {M. J.} and Shimwell, {T. W.} and D. Nisbet and V. Jelic and Callingham, {J. R.} and R{\"o}ttgering, {H. J. A.} and M. Bonato and M. Bondi and B. Ciardi and Cochrane, {R. K.} and Jarvis, {M. J.} and R. Kondapally and Koopmans, {L. V. E.} and O'Sullivan, {S. P.} and I. Prandoni and Schwarz, {D. J.} and Smith, {D. J. B.} and L. Wang and Williams, {W. L.} and S. Zaroubi",
year = "2021",
month = apr,
day = "1",
doi = "10.1051/0004-6361/202038828",
language = "English",
volume = "648",
journal = "Astronomy and Astrophysics",
issn = "0004-6361",
publisher = " EDP Sciences",
}