Research output: Contribution to journal › Article › peer-review
The LOFAR Two-metre Sky Survey: Deep Fields. II. The ELAIS-N1 LOFAR deep field. / Sabater, J.; Best, P. N.; Tasse, C.; Hardcastle, M. J.; Shimwell, T. W.; Nisbet, D.; Jelic, V.; Callingham, J. R.; Rottgering, H. J. A.; Bonato, M.; Bondi, M.; Ciardi, B.; Cochrane, R. K.; Jarvis, M. J.; Kondapally, R.; Koopmans, L. V. E.; O'Sullivan, S. P.; Prandoni, I.; Schwarz, D. J.; Smith, D. J. B.; Wang, L.; Williams, W. L.; Zaroubi, S.
In: Astronomy & Astrophysics, 31.07.2020.Research output: Contribution to journal › Article › peer-review
}
TY - JOUR
T1 - The LOFAR Two-metre Sky Survey: Deep Fields. II. The ELAIS-N1 LOFAR deep field
AU - Sabater, J.
AU - Best, P. N.
AU - Tasse, C.
AU - Hardcastle, M. J.
AU - Shimwell, T. W.
AU - Nisbet, D.
AU - Jelic, V.
AU - Callingham, J. R.
AU - Rottgering, H. J. A.
AU - Bonato, M.
AU - Bondi, M.
AU - Ciardi, B.
AU - Cochrane, R. K.
AU - Jarvis, M. J.
AU - Kondapally, R.
AU - Koopmans, L. V. E.
AU - O'Sullivan, S. P.
AU - Prandoni, I.
AU - Schwarz, D. J.
AU - Smith, D. J. B.
AU - Wang, L.
AU - Williams, W. L.
AU - Zaroubi, S.
N1 - © 2020 ESO
PY - 2020/7/31
Y1 - 2020/7/31
N2 - 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.
AB - 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.
KW - astro-ph.GA
KW - astro-ph.HE
U2 - 10.1051/0004-6361/202038828
DO - 10.1051/0004-6361/202038828
M3 - Article
JO - Astronomy & Astrophysics
JF - Astronomy & Astrophysics
SN - 0004-6361
ER -