The Galactic Faraday rotation sky 2020

Creators: Hutschenreuter, S.; Anderson, C. S.; Betti, S.; Bower, G. C.; Brown, J.-A.; Brüggen, M.; Carretti, E.; Clarke, T.; Clegg, A.; Costa, A.; Croft, S.; Eck, C. V.; Gaensler, B. M.; de Gasperin, F.; Haverkorn, M.; Heald, G.; Hull, C. L. H.; Inoue, M.; Johnston-Hollitt, M.; Kaczmarek, J. F.; Law, C. J.; Ma, Y. K.; MacMahon, D.; Mao, S. A.; Riseley, C.; Roy, S.; Shanahan, R.; Shimwell, T.; Stil, J.; Sobey, C.; O'Sullivan, S. P.; Tasse, C.; Vacca, V.; Vernstrom, T.; Williams, P. K. G.; Wright, M.; Enßlin, T. A.

Abstract

Aims. This work provides an update to existing reconstructions of the Galactic Faraday rotation sky by processing almost all Faraday rotation data sets available at the end of the year 2020. Observations of extra-Galactic sources in recent years have further illuminated the previously underconstrained southern celestial sky, as well as parts of the inner disc of the Milky Way, along with other regions. This has culminated in an all-sky data set of 55 190 data points, thereby comprising a significant expansion on the 41 330 used in previous works. At the same time, this novelty makes an updated separation of the Galactic component a promising enterprise. The increased source density allows us to present our results in a resolution of about 1.3 × 10⁻² deg² (46.8 arcmin²), which is a twofold increase compared to previous works. Methods. As for previous Faraday rotation sky reconstructions, this work is based on information field theory, namely, a Bayesian inference scheme for field-like quantities that handles noisy and incomplete data. Results. In contrast to previous reconstructions, we find a significantly thinner and pronounced Galactic disc with small-scale structures exceeding values of several thousand rad m⁻². The improvements can mainly be attributed to the new catalog of Faraday data, but are also supported by advances in correlation structure modeling within numerical information field theory. We also provide a detailed discussion on the statistical properties of the Faraday rotation sky and we investigate correlations with other data sets.

Additional Information

© ESO 2022. Received 3 February 2021; Accepted 4 October 2021; Published online 04 January 2022. The results in this publication have been derived using the NIFTy package (https://gitlab.mpcdf.mpg.de/ift/NIFTy, The NIFTy5 team, in prep.). Some of the images were produced using the CMasher library (https://github.com/1313e/CMasher, van der Velden 2020). We would like to thank Jennifer West and the CIRADA team providing the cutout server. S.H. would like to thank Philipp Frank, Philipp Arras, Martin Reinecke, Jakob Knollmüller, Reimar Leike, and the rest of the IFT team for valuable discussions and their continuous work on the NIFTy package. The noise estimation template in Fig. 8 was produced using the pygedm package (https://pypi.org/project/pygedm/, Yao et al. 2017). We thank Rainer Beck for his careful reading and valuable comments as the Max Planck Institute for Radio Astronomy (MPIfR) internal referee. S.H. and M.H. acknowledge funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No 772663). The Australia Telescope is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO. J.M.S. acknowledges the support of the Natural Sciences and Engineering Research Council of Canada (NSERC), 2019-04848. J.B. acknowledges the support of the Natural Sciences and Engineering Research Council of Canada and the National Research Council of Canada. Basic research in radio astronomy at the US Naval Research Laboratory is supported by 6.1 Base funding. C.J.R. acknowledges financial support from the ERC Starting Grant "DRANOEL", number 714245. C.L.H.H. acknowledges the support of the NAOJ Fellowship and JSPS KAKENHI grants 18K13586 and 20K14527. The Paul G. Allen Family Foundation, the US Naval Observatory and the US National Science Foundation grants AST-0321309, AST-0540690 and AST-0838268 have contributed to the ATA project. This paper has made use of the S-PASS/ATCA RM catalog Schnitzeler et al. (2019). The Dunlap Institute is funded through an endowment established by the David Dunlap family and the University of Toronto. C.V.E. and B.M.G. acknowledge the support of the Natural Sciences and Engineering Research Council of Canada (NSERC) through grant RGPIN-2015-05948, of the Canada Research Chairs program, and of the Canada Foundation for Innovation 2017 Innovation Fund through Project 35999. LOFAR (van Haarlem et al. 2013) is the Low Frequency Array designed and constructed by ASTRON. It has observing, data processing, and data storage facilities in several countries, which are owned by various parties (each with their own funding sources), and which are collectively operated by the ILT foundation under a joint scientific policy. The ILT resources have benefited from the following recent major funding sources: CNRS-INSU, Observatoire de Paris and Université d'Orléans, France; BMBF, MIWF-NRW, MPG, Germany; Science Foundation Ireland (SFI), Department of Business, Enterprise and Innovation (DBEI), Ireland; NWO, The Netherlands; The Science and Technology Facilities Council, UK; Ministry of Science and Higher Education, Poland; The Istituto Nazionale di Astrofisica (INAF), Italy. This research made use of the Dutch national e-infrastructure with support of the SURF Cooperative (e-infra 180169) and the LOFAR e-infra group. The Jülich LOFAR Long Term Archive and the German LOFAR network are both coordinated and operated by the Jülich Supercomputing Centre (JSC), and computing resources on the supercomputer JUWELS at JSC were provided by the Gauss Centre for Supercomputing e.V. (grant CHTB00) through the John von Neumann Institute for Computing (NIC). This research made use of the University of Hertfordshire high-performance computing facility and the LOFAR-UK computing facility located at the University of Hertfordshire and supported by STFC [ST/P000096/1], and of the Italian LOFAR IT computing infrastructure supported and operated by INAF, and by the Physics Department of Turin university (under an agreement with Consorzio Interuniversitario per la Fisica Spaziale) at the C3S Supercomputing Centre, Italy.

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