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First release of Apertif imaging survey data

Adams, E. A. K. and Adebahr, B. and de Blok, W. J. G. and Dénes, H. and Hess, K. M. and van der Hulst, J. M. and Kutkin, A. and Lucero, D. M. and Morganti, R. and Moss, V. A. and Oosterloo, T. A. and Orrú, E. and Schulz, R. and van Amesfoort, A. S. and Berger, A. and Boersma, O. M. and Bouwhuis, M. and van den Brink, R. and van Cappellen, W. A. and Connor, L. and Coolen, A. H. W. M. and Damstra, S. and van Diepen, G. N. J. and Dijkema, T. J. and Ebbendorf, N. and Grange, Y. G. and de Goei, R. and Gunst, A. W. and Holties, H. A. and Hut, B. and Ivashina, M. and Józsa, G. I. G. and van Leeuwen, J. and Loose, G. M. and Maan, Y. and Mancini, M. and Mika, Á. and Mulder, H. and Norden, M. J. and Offringa, A. R. and Oostrum, L. C. and Pastor-Marazuela, I. and Pisano, D. J. and Ponomareva, A. A. and Romein, J. W. and Ruiter, M. and Schoenmakers, A. P. and van der Schuur, D. and Sluman, J. J. and Smits, R. and Stuurwold, K. J. C. and Verstappen, J. and Vilchez, N. P. E. and Vohl, D. and Wierenga, K. J. and Wijnholds, S. J. and Woestenburg, E. E. M. and Zanting, A. W. and Ziemke, J. (2022) First release of Apertif imaging survey data. Astronomy and Astrophysics, 667 . Art. No. A38. ISSN 0004-6361. doi:10.1051/0004-6361/202244007.

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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 δ. 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-σ H ɪ column density sensitivity of 1.8 × 10²⁰ atoms cm⁻² over 20 km s⁻¹ (for a median angular resolution of 24″ × 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.

Item Type:Article
Related URLs:
URLURL TypeDescription
Adams, E. A. K.0000-0002-9798-5111
Adebahr, B.0000-0002-5447-6878
de Blok, W. J. G.0000-0001-8957-4518
Dénes, H.0000-0002-9214-8613
Hess, K. M.0000-0001-9662-9089
van der Hulst, J. M.0000-0002-9316-763X
Kutkin, A.0000-0002-1123-7498
Lucero, D. M.0000-0002-9288-9331
Morganti, R.0000-0002-9482-6844
Moss, V. A.0000-0002-3005-9738
Oosterloo, T. A.0000-0002-0616-6971
Boersma, O. M.0000-0002-7925-9503
Bouwhuis, M.0000-0001-6512-3683
van Cappellen, W. A.0000-0002-3390-2268
Connor, L.0000-0002-7587-6352
Dijkema, T. J.0000-0001-7551-4493
Grange, Y. G.0000-0001-5125-9539
Gunst, A. W.0000-0003-0248-649X
Holties, H. A.0000-0002-8436-0534
Ivashina, M.0000-0002-6584-1826
Józsa, G. I. G.0000-0003-0608-6258
van Leeuwen, J.0000-0001-8503-6958
Loose, G. M.0000-0003-4721-747X
Maan, Y.0000-0002-0862-6062
Mancini, M.0000-0002-3861-9234
Mika, Á.0000-0003-0666-2032
Offringa, A. R.0000-0002-5809-2783
Oostrum, L. C.0000-0001-8724-8372
Pastor-Marazuela, I.0000-0002-4357-8027
Pisano, D. J.0000-0001-7996-7860
Schoenmakers, A. P.0000-0002-8606-3955
van der Schuur, D.0000-0002-9142-1411
Vohl, D.0000-0003-1779-4532
Wijnholds, S. J.0000-0002-0463-3011
Zanting, A. W.0000-0002-4238-4618
Additional Information:We wish to thank the anonymous referee for useful comments that improved the quality and structure of this paper. This work makes use of data from the Apertif system installed at the Westerbork Synthesis Radio Telescope owned by ASTRON. ASTRON, the Netherlands Institute for Radio Astronomy, is an institute of the Dutch Research Council (“De Nederlandse Organisatie voor Wetenschappelijk Onderzoek, NWO). Apertif was partly financed by the NWO Groot projects Apertif (175.010.2005.015) and Apropos (175.010.2009.012). This work was partly supported by funding from the European Research Council under the European Union’s Seventh Frame-work Programme (FP/2007-2013), through ERC Grant Agreement No. 291531 (‘HIStoryNU’, PI: JMvdH) and ERC Advanced Grant RADIOLIFE-320745 (PI: RM), in addition to funding from NWO via grant TOP1EW.14.105 (PI: TAO). E.A.K.A. is supported by the WISE research programme, which is financed by NWO. B.A. acknowledges funding from the German Science Foundation DFG, within the Collaborative Research Center SFB1491 “Cosmic Interacting Matters - From Source to Signal”. KMH acknowledges financial support from the State Agency for Research of the Spanish Ministry of Science, Innovation and Universities through the “Center of Excellence Severo Ochoa” awarded to the Instituto de Astrofísica de Andalucía (SEV-2017-0709), from the coordination of the participation in SKA-SPAIN, funded by the Ministry of Science and Innovation (MCIN). OMB and JvL acknowledge funding from NWO under the Vici research program “ARGO” with project number 639.043.815. Y.M., L.C.O., R.S. and J.vL. acknowledge funding from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013)/ERC Grant Agreement No. 617199 (“ALERT”). IPM acknowledges funding from the Netherlands Research School for Astronomy (grant no. NOVA5-NW3- A.A.P. acknowledges support of the STFC consolidated grant ST/S000488/1. DV acknowledges support from the Netherlands eScience Center (NLeSC) under grant ASDI.15.406. This research has made use of NASA’s Astrophysics Data System Bibliographic Services and Astropy, ( a community-developed core Python package for Astronomy (Astropy Collaboration 2013, 2018).
Funding AgencyGrant Number
Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)175.010.2005.015
Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)175.010.2009.012
European Research Council (ERC)291531
European Research Council (ERC)320745
Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)TOP1EW.14.105
Deutsche Forschungsgemeinschaft (DFG)SFB1491
Severo OchoaSEV-2017-0709
Ministerio de Ciencia e Innovación (MCIN)UNSPECIFIED
Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)639.043.815
European Research Council (ERC)617199
Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)NOVA5-NW3-
Science and Technology Facilities Council (STFC)ST/S000488/1
Netherlands eScience CenterASDI.15.406
Record Number:CaltechAUTHORS:20221121-712406200.22
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ID Code:117957
Deposited By: Research Services Depository
Deposited On:02 Dec 2022 16:39
Last Modified:02 Dec 2022 18:23

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