The LOFAR Two-metre Sky Survey: V. Second data release
Journal article, 2022
In this data release from the ongoing LOw-Frequency ARray (LOFAR) Two-metre Sky Survey we present 120a 168 MHz images covering 27% of the northern sky. Our coverage is split into two regions centred at approximately 12h45m +44 30a and 1h00m +28 00a and spanning 4178 and 1457 square degrees respectively. The images were derived from 3451 h (7.6 PB) of LOFAR High Band Antenna data which were corrected for the direction-independent instrumental properties as well as direction-dependent ionospheric distortions during extensive, but fully automated, data processing. A catalogue of 4 396 228 radio sources is derived from our total intensity (Stokes I) maps, where the majority of these have never been detected at radio wavelengths before. At 6a resolution, our full bandwidth Stokes I continuum maps with a central frequency of 144 MHz have: a median rms sensitivity of 83 μJy beama 1; a flux density scale accuracy of approximately 10%; an astrometric accuracy of 0.2a; and we estimate the point-source completeness to be 90% at a peak brightness of 0.8 mJy beama 1. By creating three 16 MHz bandwidth images across the band we are able to measure the in-band spectral index of many sources, albeit with an error on the derived spectral index of > a ±a 0.2 which is a consequence of our flux-density scale accuracy and small fractional bandwidth. Our circular polarisation (Stokes V) 20a resolution 120a168 MHz continuum images have a median rms sensitivity of 95 μJy beama 1, and we estimate a Stokes I to Stokes V leakage of 0.056%. Our linear polarisation (Stokes Q and Stokes U) image cubes consist of 480a A a 97.6 kHz wide planes and have a median rms sensitivity per plane of 10.8 mJy beama 1 at 4a and 2.2 mJy beama 1 at 20a; we estimate the Stokes I to Stokes Q/U leakage to be approximately 0.2%. Here we characterise and publicly release our Stokes I, Q, U and V images in addition to the calibrated uv-data to facilitate the thorough scientific exploitation of this unique dataset.
Techniques: image processing
Surveys
Catalogs
Radio continuum: general
Author
T. W. Shimwell
Netherlands Institute for Radio Astronomy (ASTRON)
M. J. Hardcastle
University of Hertfordshire
C. Tasse
Paris Observatory
P. N. Best
University of Edinburgh
H. J.A. Röttgering
Leiden University
W. L. Williams
Leiden University
A. Botteon
Leiden University
A. Drabent
Thüringer Landessternwarte Tautenburg
A. P. Mechev
Leiden University
A. Shulevski
Leiden University
R. van Weeren
Leiden University
L. Bester
Rhodes University
M. Bruggen
University of Hamburg
G. Brunetti
Istituto di Radioastronomia
J. R. Callingham
Netherlands Institute for Radio Astronomy (ASTRON)
K.T. Chyz̊y
Jagiellonian University in Kraków
John Conway
Chalmers, Space, Earth and Environment, Onsala Space Observatory
T. J. Dijkema
Netherlands Institute for Radio Astronomy (ASTRON)
K. Duncan
University of Edinburgh
F. De Gasperin
University of Hamburg
C. Hale
University of Edinburgh
M. Haverkorn
Radboud University
B. Hugo
Rhodes University
N. Jackson
University of Manchester
M. Mevius
Netherlands Institute for Radio Astronomy (ASTRON)
G. K. Miley
Leiden University
L. Morabito
Durham University
R. Morganti
Netherlands Institute for Radio Astronomy (ASTRON)
A. R. Offringa
Netherlands Institute for Radio Astronomy (ASTRON)
J. B. R. Oonk
Netherlands Institute for Radio Astronomy (ASTRON)
D. Rafferty
University of Hamburg
J. Sabater
University of Edinburgh
D.J.B. Smith
University of Hertfordshire
D. J. Schwarz
Bielefeld University
O. Smirnov
Rhodes University
S.P. Oasullivan
Dublin City University
Harish K. Vedantham
Netherlands Institute for Radio Astronomy (ASTRON)
G.J. White
STFC Rutherford Appleton Laboratory
J.G. Albert
Leiden University
L. Alegre
University of Edinburgh
B. Asabere
Netherlands Institute for Radio Astronomy (ASTRON)
D.J. Bacon
University of Portsmouth
A. Bonafede
University of Hamburg
E. Bonnassieux
University of Bologna
M. Brienza
Istituto di Radioastronomia
M. Bilicki
Polish Academy of Sciences
M. Bonato
Istituto di Radioastronomia
G. Calistro Rivera
European Southern Observatory (ESO)
R. Cassano
Istituto di Radioastronomia
R. Cochrane
Harvard-Smithsonian Center for Astrophysics
J. H. Croston
Open University
V. Cuciti
University of Hamburg
D. Dallacasa
Istituto di Radioastronomia
A. Danezi
SURFnet
R. -J. Dettmar
Ruhr-Universität Bochum
G. Di Gennaro
University of Hamburg
H.W. Edler
University of Hamburg
T.A. Enalin
Max Planck Society
K.L. Emig
National Radio Astronomy Observatory
T. M.O. Franzen
Netherlands Institute for Radio Astronomy (ASTRON)
C. García-Vergara
Leiden University
Y. G. Grange
Netherlands Institute for Radio Astronomy (ASTRON)
G. Gurkan
Thüringer Landessternwarte Tautenburg
M. Hajduk
Radboud University
G. Heald
Commonwealth Scientific and Industrial Research Organisation (CSIRO)
V. Heesen
University of Hamburg
D. N. Hoang
University of Hamburg
M. Hoeft
Thüringer Landessternwarte Tautenburg
Cathy Horellou
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
M. Iacobelli
Netherlands Institute for Radio Astronomy (ASTRON)
M. Jamrozy
Jagiellonian University in Kraków
V. Jelia
Ruder Boskovic Institute
R. Kondapally
University of Edinburgh
P. Kukreti
Netherlands Institute for Radio Astronomy (ASTRON)
M. Kunert-Bajraszewska
Nicolaus Copernicus University
M. Magliocchetti
Istituto nazionale di astrofisica (INAF)
V. Mahatma
Thüringer Landessternwarte Tautenburg
K. Maaek
Narodowe Centrum Badan Jadrowych
S. Mandal
Leiden University
F. Massaro
University of Turin
Z. Meyer-Zhao
Netherlands Institute for Radio Astronomy (ASTRON)
B. Mingo
Open University
R.I.J. Mostert
Netherlands Institute for Radio Astronomy (ASTRON)
Dhanya G. Nair
Joint Institute for VLBI in Europe (JIVE)
S.J. Nakoneczny
Narodowe Centrum Badan Jadrowych
B. Nikiel-Wroczyaski
Jagiellonian University in Kraków
E. Orrú
Netherlands Institute for Radio Astronomy (ASTRON)
U. Pajdosz-Amierciak
Jagiellonian University in Kraków
T. Pasini
University of Hamburg
I. Prandoni
Istituto di Radioastronomia
H.E. Van Piggelen
SURFnet
K. Rajpurohit
Istituto di Radioastronomia
E. Retana-Montenegro
University of KwaZulu-Natal
C. J. Riseley
Istituto di Radioastronomia
A. Rowlinson
Netherlands Institute for Radio Astronomy (ASTRON)
A. Saxena
University College London (UCL)
C. Schrijvers
SURFnet
F. Sweijen
Leiden University
T.M. Siewert
Bielefeld University
R. Timmerman
Leiden University
M. Vaccari
Istituto di Radioastronomia
J. Vink
Anton Pannekoek Institute for Astronomy
Jennifer L. West
University of Toronto
A. Woaowska
Commonwealth Scientific and Industrial Research Organisation (CSIRO)
X. Zhang
Leiden University
J. Zheng
University of Portsmouth
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 659 A1Subject Categories
Geophysics
Signal Processing
Medical Image Processing
DOI
10.1051/0004-6361/202142484