First release of Apertif imaging survey data
Journal article, 2022
Context. Apertif is a phased-array feed system for the Westerbork Synthesis Radio Telescope, providing forty instantaneous beams over 300 MHz of bandwidth. A dedicated survey program utilizing this upgrade started on 1 July 2019, with the last observations taken on 28 February 2022. The imaging survey component provides radio continuum, polarization, and spectral line data. Aims. Public release of data is critical for maximizing the legacy of a survey. Toward that end, we describe the release of data products from the first year of survey operations, through 30 June 2020. In particular, we focus on defining quality control metrics for the processed data products. Methods. The Apertif imaging pipeline, Apercal, automatically produces non-primary beam corrected continuum images, polarization images and cubes, and uncleaned spectral line and dirty beam cubes for each beam of an Apertif imaging observation. For this release, processed data products are considered on a beam-by-beam basis within an observation. We validate the continuum images by using metrics that identify deviations from Gaussian noise in the residual images. If the continuum image passes validation, we release all processed data products for a given beam. We apply further validation to the polarization and line data products and provide flags indicating the quality of those data products. Results. We release all raw observational data from the first year of survey observations, for a total of 221 observations of 160 independent target fields, covering approximately one thousand square degrees of sky. Images and cubes are released on a per beam basis, and 3374 beams (of 7640 considered) are released. The median noise in the continuum images is 41.4 uJy beam(-1), with a slightly lower median noise of 36.9 uJy beam(-1) in the Stokes V polarization image. The median angular resolution is 11.6 ''/sin delta. The median noise for all line cubes, with a spectral resolution of 36.6 kHz, is 1.6 mJy beam(-1), corresponding to a 3-sigma H i column density sensitivity of 1.8 x 10(20) atoms cm(-2) over 20 km s(-1) (for a median angular resolution of 24 '' x 15 ''). Line cubes at lower frequency have slightly higher noise values, consistent with the global RFI environment and overall Apertif system performance. We also provide primary beam images for each individual Apertif compound beam. The data are made accessible using a Virtual Observatory interface and can be queried using a variety of standard tools.
radio lines
galaxies
galaxies
surveys
radio continuum
ISM
polarization
galaxies
Author
E. A. K. Adams
Netherlands Institute for Radio Astronomy (ASTRON)
Kapteyn Astronomical Institute
B. Adebahr
Ruhr-Universität Bochum
W. J. G. de Blok
Netherlands Institute for Radio Astronomy (ASTRON)
University of Cape Town
Kapteyn Astronomical Institute
H. Denes
Netherlands Institute for Radio Astronomy (ASTRON)
K. M. Hess
Kapteyn Astronomical Institute
Institute of Astrophysics of Andalusia (IAA)
Netherlands Institute for Radio Astronomy (ASTRON)
J. M. van der Hulst
Kapteyn Astronomical Institute
A. Kutkin
Russian Academy of Sciences
Netherlands Institute for Radio Astronomy (ASTRON)
D. M. Lucero
Virginia Polytechnic Institute and State University
R. Morganti
Kapteyn Astronomical Institute
Netherlands Institute for Radio Astronomy (ASTRON)
V. A. Moss
Commonwealth Scientific and Industrial Research Organisation (CSIRO)
Netherlands Institute for Radio Astronomy (ASTRON)
The University of Sydney
T. A. Oosterloo
Netherlands Institute for Radio Astronomy (ASTRON)
Kapteyn Astronomical Institute
E. Orru
Netherlands Institute for Radio Astronomy (ASTRON)
R. Schulz
Netherlands Institute for Radio Astronomy (ASTRON)
A. S. van Amesfoort
Netherlands Institute for Radio Astronomy (ASTRON)
A. Berger
Ruhr-Universität Bochum
O. M. Boersma
University of Amsterdam
M. Bouwhuis
National Institute for Subatomic Physics (NIKHEF)
R. van den Brink
Netherlands Institute for Radio Astronomy (ASTRON)
Tricas Industrial Design & Engineering
W. A. van Cappellen
Netherlands Institute for Radio Astronomy (ASTRON)
L. Connor
University of Amsterdam
California Institute of Technology (Caltech)
A. H. W. M. Coolen
Netherlands Institute for Radio Astronomy (ASTRON)
S. Damstra
Netherlands Institute for Radio Astronomy (ASTRON)
G. N. J. van Diepen
Netherlands Institute for Radio Astronomy (ASTRON)
T. J. Dijkema
Netherlands Institute for Radio Astronomy (ASTRON)
N. Ebbendorf
Netherlands Institute for Radio Astronomy (ASTRON)
Y. G. Grange
Netherlands Institute for Radio Astronomy (ASTRON)
R. de Goei
Netherlands Institute for Radio Astronomy (ASTRON)
A. W. Gunst
Netherlands Institute for Radio Astronomy (ASTRON)
H. A. Holties
Netherlands Institute for Radio Astronomy (ASTRON)
B. Hut
Netherlands Institute for Radio Astronomy (ASTRON)
Marianna Ivashina
Chalmers, Electrical Engineering, Communication, Antennas and Optical Networks
G. I. G. Jozsa
Max Planck Society
Rhodes University
J. van Leeuwen
Netherlands Institute for Radio Astronomy (ASTRON)
University of Amsterdam
G. M. Loose
Netherlands Institute for Radio Astronomy (ASTRON)
Y. Maan
Tata Institute of Fundamental Research
Netherlands Institute for Radio Astronomy (ASTRON)
M. Mancini
Netherlands Institute for Radio Astronomy (ASTRON)
A. Mika
Netherlands Institute for Radio Astronomy (ASTRON)
H. Mulder
Netherlands Institute for Radio Astronomy (ASTRON)
M. J. Norden
Netherlands Institute for Radio Astronomy (ASTRON)
A. R. Offringa
Netherlands Institute for Radio Astronomy (ASTRON)
Kapteyn Astronomical Institute
L. C. Oostrum
University of Amsterdam
Netherlands Institute for Radio Astronomy (ASTRON)
Netherlands eScience Center
I Pastor-Marazuela
Netherlands Institute for Radio Astronomy (ASTRON)
University of Amsterdam
D. J. Pisano
West Virginia University
University of Cape Town
A. A. Ponomareva
University of Oxford
J. W. Romein
Netherlands Institute for Radio Astronomy (ASTRON)
M. Ruiter
Netherlands Institute for Radio Astronomy (ASTRON)
A. P. Schoenmakers
Netherlands Institute for Radio Astronomy (ASTRON)
D. van der Schuur
Netherlands Institute for Radio Astronomy (ASTRON)
J. J. Sluman
Netherlands Institute for Radio Astronomy (ASTRON)
R. Smits
Netherlands Institute for Radio Astronomy (ASTRON)
K. J. C. Stuurwold
Netherlands Institute for Radio Astronomy (ASTRON)
J. Verstappen
Netherlands Institute for Radio Astronomy (ASTRON)
Kapteyn Astronomical Institute
N. P. E. Vilchez
Netherlands Institute for Radio Astronomy (ASTRON)
D. Vohl
University of Amsterdam
Netherlands Institute for Radio Astronomy (ASTRON)
K. J. Wierenga
Netherlands Institute for Radio Astronomy (ASTRON)
S. J. Wijnholds
Netherlands Institute for Radio Astronomy (ASTRON)
E. E. M. Woestenburg
Netherlands Institute for Radio Astronomy (ASTRON)
A. W. Zanting
Netherlands Institute for Radio Astronomy (ASTRON)
J. Ziemke
Netherlands Institute for Radio Astronomy (ASTRON)
University of Oslo
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 667 A38Subject Categories
Remote Sensing
Computer Vision and Robotics (Autonomous Systems)
Medical Image Processing
DOI
10.1051/0004-6361/202244007