Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Article
  • Published:

Characterization of the decametre sky at subarcminute resolution

Abstract

The largely unexplored decametre radio band (10–30 MHz) provides a unique window for studying a range of astronomical topics, such as auroral emission from exoplanets, inefficient cosmic ray acceleration mechanisms and fossil radio plasma. The scarcity of low-frequency studies is mainly due to severe ionospheric corruption. Here we present a calibration strategy to correct for the ionosphere in the decametre band. We apply this to an observation from the Low-Frequency Array (LOFAR) between 16 and 30 MHz. The resulting image covers 330 square degrees of sky at a resolution of 45″, reaching a sensitivity of 12 mJy per beam, which is an improvement by an order of magnitude in terms of sensitivity and resolution compared to previous decametre observations. Residual ionospheric effects cause additional blurring between 60″ and 100″. We have identified four fossil plasma sources in the surveyed region. These sources probably harbour rejuvenated radio plasma from past active galactic nuclei outbursts. Three are near the centre of low-mass galaxy clusters. Notably, two of these sources display the steepest radio spectral index among all the sources detected at 23 MHz. This indicates that fossil plasma sources constitute the primary population of steep-spectrum sources at these frequencies, emphasizing the large discovery potential of ground-based decametre observations.

This is a preview of subscription content, access via your institution

Access options

Buy this article

Prices may be subject to local taxes which are calculated during checkout

Fig. 1: Comparison of the RMS noise and central frequency of previous low-frequency observations.
Fig. 2: Overview of our observed region.
Fig. 3: Fraction of LOFAR data flagged due to RFI as a function of frequency.
Fig. 4: Euclidean normalized source counts in the surveyed area.
Fig. 5: Images of four re-energized fossil plasma sources detected at 23 MHz.

Similar content being viewed by others

Data availability

The catalogue produced in this work is available in the Supplementary Data. The calibrated mosaic image is available upon reasonable request to the authors.

Code availability

The following codes were used in this work and are readily available: https://github.com/saopicc/DDFacet (DDFacet); https://git.astron.nl/RD/DP3 (DP3); https://gitlab.com/aroffringa/wsclean (WSClean); https://github.com/rvweeren/lofar_facet_selfcal (facetselfcal); and https://github.com/lofar-astron/PyBDSF (PyBDSF). Other code used in this work is available upon request to the authors.

References

  1. Jansky, K. G. Directional studies of atmospherics at high frequencies. Proc. Inst. Radio Eng. 20, 1920–1932 (1932).

    Google Scholar 

  2. Odegard, N. Decameter wavelength observations of the Rosette nebula and the Monoceros loop supernova remnant. Astrophys. J. 301, 813 (1986).

    ADS  Google Scholar 

  3. Callingham, J. R. et al. Broadband spectral modeling of the extreme gigahertz-peaked spectrum radio source PKS B0008-421. Astrophys. J. 809, 168 (2015).

    ADS  Google Scholar 

  4. Callingham, J. R. et al. Low-frequency monitoring of flare star binary CR Draconis: long-term electron-cyclotron maser emission. Astron. Astrophys. 648, A13 (2021).

    Google Scholar 

  5. Zarka, P. Auroral radio emissions at the outer planets: observations and theories. J. Geophys. Res. 103, 20159–20194 (1998).

    ADS  Google Scholar 

  6. Zarka, P. Radio and plasma waves at the outer planets. Adv. Space Res. 33, 2045–2060 (2004).

    ADS  Google Scholar 

  7. Vedantham, H. K. et al. Coherent radio emission from a quiescent red dwarf indicative of star–planet interaction. Nat. Astron. 4, 577–583 (2020).

    ADS  Google Scholar 

  8. Cassano, R. & Brunetti, G. Cluster mergers and non-thermal phenomena: a statistical magneto-turbulent model. Mon. Not. R. Astron. Soc. 357, 1313–1329 (2005).

    ADS  Google Scholar 

  9. Enßlin, T. A. & Krishna, G. Reviving fossil radio plasma in clusters of galaxies by adiabatic compression in environmental shock waves. Astron. Astrophys. 366, 26–34 (2001).

    ADS  Google Scholar 

  10. de Gasperin, F. et al. Gentle reenergization of electrons in merging galaxy clusters. Sci. Adv. 3, e1701634 (2017).

    ADS  Google Scholar 

  11. Brienza, M. et al. A snapshot of the oldest active galactic nuclei feedback phases. Nat. Astron. 5, 1261–1267 (2021).

    ADS  Google Scholar 

  12. Enßlin, T. A. & Brüggen, M. On the formation of cluster radio relics. Mon. Not. R. Astron. Soc. 331, 1011–1019 (2002).

    ADS  Google Scholar 

  13. Offringa, A. R. et al. The LOFAR radio environment. Astron. Astrophys. 549, A11 (2013).

    Google Scholar 

  14. Salas, P. et al. LOFAR observations of decameter carbon radio recombination lines towards Cassiopeia A. Mon. Not. R. Astron. Soc. 467, 2274–2287 (2017).

    ADS  Google Scholar 

  15. de Gasperin, F., Mevius, M., Rafferty, D. A., Intema, H. T. & Fallows, R. A. The effect of the ionosphere on ultra-low-frequency radio-interferometric observations. Astron. Astrophys. 615, A179 (2018).

    Google Scholar 

  16. Ellis, G. R. A. & Hamilton, P. A. Cosmic radio noise survey at 4.7 Mc/s. Astrophys. J. 143, 227 (1966).

    ADS  Google Scholar 

  17. Bentum, M. J. et al. A roadmap towards a space-based radio telescope for ultra-low frequency radio astronomy. Adv. Space Res. 65, 856–867 (2020).

    ADS  Google Scholar 

  18. Kassim, N. E. The Clark Lake 30.9 MHz Galactic Plane Survey. Astrophys. J. Suppl. Ser. 68, 715 (1988).

    ADS  Google Scholar 

  19. Braude, S. I., Megn, A. V., Riabov, B. P., Sharykin, N. K. & Zhuk, I. N. Decametric survey of discrete sources in the northern sky. I: The UTR-2 Radio Telescope. Experimental techniques and data processing. Astrophys. Space Sci. 54, 3–36 (1978).

    ADS  Google Scholar 

  20. Roger, R. S., Costain, C. H., Landecker, T. L. & Swerdlyk, C. M. The radio emission from the Galaxy at 22 MHz. Astron. Astrophys. Suppl. Ser. 137, 7–19 (1999).

    ADS  Google Scholar 

  21. Hales, S. E. G., Waldram, E. M., Rees, N. & Warner, P. J. A revised machine-readable source list for the Rees 38-MHz survey. Mon. Not. R. Astron. Soc. 274, 447–451 (1995).

    ADS  Google Scholar 

  22. van Haarlem, M. P. et al. LOFAR: the low-frequency array. Astron. Astrophys. 556, A2 (2013).

    Google Scholar 

  23. Shimwell, T. W. et al. The LOFAR Two-metre Sky Survey. I. Survey description and preliminary data release. Astron. Astrophys. 598, A104 (2017).

    Google Scholar 

  24. Shimwell, T. W. et al. The LOFAR Two-metre Sky Survey. V. Second data release. Astron. Astrophys. 659, A1 (2022).

    Google Scholar 

  25. de Gasperin, F. et al. The LOFAR LBA Sky Survey. I. Survey description and preliminary data release. Astron. Astrophys. 648, A104 (2021).

    Google Scholar 

  26. de Gasperin, F. et al. The LOFAR LBA Sky Survey II. First data release. Astron. Astrophys. 673, A165 (2023).

  27. van Weeren, R. J. et al. LOFAR Facet Calibration. Astrophys. J. Suppl. Ser. 223, 2 (2016).

    ADS  Google Scholar 

  28. Intema, H. T., Jagannathan, P., Mooley, K. P. & Frail, D. A. The GMRT 150 MHz all-sky radio survey. First alternative data release TGSS ADR1. Astron. Astrophys. 598, A78 (2017).

    ADS  Google Scholar 

  29. Mohan, N. & Rafferty, D. PyBDSF: Python Blob Detection and Source Finder, record ascl:1502.007 1502.007 (Astrophysics Source Code Library, 2015).

  30. de Zotti, G., Massardi, M., Negrello, M. & Wall, J. Radio and millimeter continuum surveys and their astrophysical implications. Astron. Astrophys. Rev. 18, 1–65 (2010).

    ADS  Google Scholar 

  31. Condon, J. J., Cotton, W. D. & Broderick, J. J. Radio sources and star formation in the local Universe. Astron. J. 124, 675–689 (2002).

    ADS  Google Scholar 

  32. van Weeren, R. J. et al. LOFAR low-band antenna observations of the 3C 295 and Boötes fields: source counts and ultra-steep spectrum sources. Astrophys. J. 793, 82 (2014).

    ADS  Google Scholar 

  33. Harwood, J. J., Hardcastle, M. J. & Croston, J. H. Spectral ageing in the lobes of cluster-centre FR II radio galaxies. Mon. Not. R. Astron. Soc. 454, 3403–3422 (2015).

    ADS  Google Scholar 

  34. Planck Collaboration. Planck 2015 results. XXVII. The second Planck catalogue of Sunyaev–Zeldovich sources. Astron. Astrophys. 594, A27 (2016).

    Google Scholar 

  35. Dálya, G. et al. GLADE: a galaxy catalogue for multimessenger searches in the advanced gravitational-wave detector era. Mon. Not. R. Astron. Soc. 479, 2374–2381 (2018).

    ADS  Google Scholar 

  36. Piffaretti, R., Arnaud, M., Pratt, G. W., Pointecouteau, E. & Melin, J. B. The MCXC: a meta-catalogue of X-ray detected clusters of galaxies. Astron. Astrophys. 534, A109 (2011).

    ADS  Google Scholar 

  37. Mandal, S. Revealing the Nature of New Low-frequency Radio Source Populations. PhD thesis, Leiden Univ. (2020).

  38. van Weeren, R. J. et al. Diffuse radio emission from galaxy clusters. Space Sci. Rev. 215, 16 (2019).

    ADS  Google Scholar 

  39. Slee, O. B., Roy, A. L., Murgia, M., Andernach, H. & Ehle, M. Four extreme relic radio sources in clusters of galaxies. Astron. J. 122, 1172–1193 (2001).

    ADS  Google Scholar 

  40. Mandal, S. et al. Revived fossil plasma sources in galaxy clusters. Astron. Astrophys. 634, A4 (2020).

    Google Scholar 

  41. Reber, G. & Ellis, G. R. Cosmic radio-frequency radiation near one megacycle. J. Geophys. Res. 61, 1–10 (1956).

    ADS  Google Scholar 

  42. Offringa, A. R., van de Gronde, J. J. & Roerdink, J. B. T. M. A morphological algorithm for improved radio-frequency interference detection. Astron. Astrophys. 539, A95 (2012).

    Google Scholar 

  43. van der Tol, S., Jeffs, B. D. & van der Veen, A. J. Self-calibration for the LOFAR radio astronomical array. IEEE Trans. Signal Process. 55, 4497–4510 (2007).

    ADS  MathSciNet  Google Scholar 

  44. Groeneveld, C. et al. Pushing sub-arcsecond resolution imaging down to 30 MHz with the trans-European International LOFAR Telescope. Astron. Astrophys. 658, A9 (2022).

    Google Scholar 

  45. Groves, K. M. et al. Equatorial scintillation and systems support. Radio Sci. 32, 2047–2064 (1997).

    ADS  Google Scholar 

  46. Lane, W. M. et al. The Very Large Array Low-frequency Sky Survey Redux (VLSSr). Mon. Not. R. Astron. Soc. 440, 327–338 (2014).

    ADS  Google Scholar 

  47. van Diepen, G., Dijkema, T. J. & Offringa, A. DPPP: Default Pre-Processing Pipeline, record ascl:1804.003 1804.003 (Astrophysics Source Code Library, 2018).

  48. Offringa, A. R. et al. WSCLEAN: an implementation of a fast, generic wide-field imager for radio astronomy. Mon. Not. R. Astron. Soc. 444, 606–619 (2014).

    ADS  Google Scholar 

  49. van Weeren, R. J. et al. LOFAR observations of galaxy clusters in HETDEX. Extraction and self-calibration of individual LOFAR targets. Astron. Astrophys. 651, A115 (2021).

    Google Scholar 

  50. Tasse, C. et al. Faceting for direction-dependent spectral deconvolution. Astron. Astrophys. 611, A87 (2018).

    Google Scholar 

  51. Zarka, P. Plasma interactions of exoplanets with their parent star and associated radio emissions. Planet. Space Sci. 55, 598–617 (2007).

    ADS  Google Scholar 

  52. Harris, D. E., Dewdney, P. E., Costain, C. H., McHardy, I. & Willis, A. G. An X-ray and radio study of steep-spectrum radio sources. I. Four fields from the Clark Lake Observatory 26 MHz Survey. Astrophys. J. 325, 610 (1988).

    ADS  Google Scholar 

  53. Williams, W. L. et al. The LOFAR LBA Sky Survey: deep fields. I. The Boötes field. Astron. Astrophys. 655, A40 (2021).

    Google Scholar 

  54. Cohen, A. S., Röttgering, H. J. A., Jarvis, M. J., Kassim, N. E. & Lazio, T. J. W. A deep, high-resolution survey at 74 MHz. Astrophys. J. Suppl. Ser. 150, 417–430 (2004).

    ADS  Google Scholar 

  55. Duchesne, S. W., Johnston-Hollitt, M., Riseley, C. J., Bartalucci, I. & Keel, S. R. The merging galaxy cluster Abell 3266 at low radio frequencies. Mon. Not. R. Astron. Soc. 511, 3525–3535 (2022).

    ADS  Google Scholar 

  56. Hurley-Walker, N. et al. GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey. I. A low-frequency extragalactic catalogue. Mon. Not. R. Astron. Soc. 464, 1146–1167 (2017).

    ADS  Google Scholar 

  57. Intema, H. T., van Weeren, R. J., Röttgering, H. J. A. & Lal, D. V. Deep low-frequency radio observations of the NOAO Boötes field. I. Data reduction and catalog construction. Astron. Astrophys. 535, A38 (2011).

    Google Scholar 

  58. Sabater, J. et al. The LOFAR Two-meter Sky Survey: Deep Fields Data Release 1. II. The ELAIS-N1 LOFAR deep field. Astron. Astrophys. 648, A2 (2021).

    Google Scholar 

  59. Mandal, S. et al. Extremely deep 150 MHz source counts from the LoTSS deep fields. Astron. Astrophys. 648, A5 (2021).

    Google Scholar 

  60. Chambers, K. C. et al. The Pan-STARRS1 Surveys. Preprint at https://arxiv.org/abs/1612.05560 (2016).

  61. Astropy Collaboration. Astropy: a community Python package for astronomy. Astron. Astrophys. 558, A33 (2013).

    Google Scholar 

  62. Astropy Collaboration. The Astropy project: building an open-science project and status of the v2.0 core package. Astron. J. 156, 123 (2018).

    ADS  Google Scholar 

  63. Astropy Collaboration. The Astropy project: sustaining and growing a community-oriented open-source project and the latest major release (v5.0) of the core package. Astrophys. J. 935, 167 (2022).

    ADS  Google Scholar 

Download references

Acknowledgements

C.G. and R.J.v.W. acknowledge support from the European Research Council (Starting Grant ClusterWeb No. 804208). M.B. is funded by the German Research Foundation under Germany’s Excellence Strategy (Project EXC 2121, Quantum Universe, 390833306). E.O. acknowledges support from the VIDI research programme (Project No. 639.042.729), which is financed by the Netherlands Organisation for Scientific Research. A.B. acknowledges financial support from the Next Generation programme of the European Union. LOFAR was 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 are collectively operated by the ILT Foundation under a joint scientific policy. The ILT resources have benefitted from the following recent major funding sources: the National Institute for Earth Sciences and Astronomy of the National Centre for Scientific Research, the Paris Observatory and the University of Orléans, France; the Federal Ministry of Education and Research, the Ministry of Innovation, Science and Research of North Rhine-Westphalia and the Max Planck Society, Germany; Science Foundation Ireland, Department of Business, Enterprise and Innovation, Ireland; the Netherlands Organisation for Scientific Research, the Netherlands; the Science and Technology Facilities Council, UK; Ministry of Science and Higher Education, Poland; and the Italian National Institute for Astrophysics, Italy. The Pan-STARRS1 Surveys (PS1) and the PS1 public science archive have been made possible through contributions by the Institute for Astronomy, the University of Hawaii, the Pan-STARRS Project Office, the Max Planck Society and its participating institutes (the Max Planck Institute for Astronomy, Heidelberg, and the Max Planck Institute for Extraterrestrial Physics, Garching), Johns Hopkins University, Durham University, the University of Edinburgh, Queen’s University Belfast, the Harvard-Smithsonian Center for Astrophysics, Las Cumbres Observatory Global Telescope Network Incorporated, the National Central University of Taiwan, the Space Telescope Science Institute, NASA (Grant No. NNX08AR22G issued through the Planetary Science Division of the NASA Science Mission Directorate), the US National Science Foundation (NSF; Grant No. AST-1238877), the University of Maryland, Eotvos Lorand University, Los Alamos National Laboratory, and the Gordon and Betty Moore Foundation. When using data from the Legacy Surveys in papers, please use the following acknowledgment: The Legacy Surveys consist of three individual and complementary projects: the Dark Energy Camera Legacy Survey (DECaLS; Proposal ID 2014B-0404; PIs D. Schlegel and A. Dey), the Beijing–Arizona Sky Survey (BASS; National Optical Astronomy Observatory, Prop. ID 2015A-0801; PIs Z. Xu and X. Fan) and the Mayall z-band Legacy Survey (Prop. ID 2016A-0453; PI A. Dey). DECaLS, BASS and the Mayall z-band Legacy Survey together include data obtained, respectively, at the Blanco telescope, Cerro Tololo Inter-American Observatory, NSF’s NOIRLab; the Bok telescope, Steward Observatory, University of Arizona; and the Mayall telescope, Kitt Peak National Observatory, NOIRLab. Pipeline processing and analyses of the data were supported by NOIRLab and Lawrence Berkeley National Laboratory (LBNL). The Legacy Surveys project is honoured to be permitted to conduct astronomical research on Iolkam Du’ag (Kitt Peak), a mountain with particular significance to the Tohono O’odham Nation. NOIRLab is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the NSF. LBNL is managed by the Regents of the University of California under contract to the US Department of Energy (DOE). This project used data obtained with the Dark Energy Camera (DECam), which was constructed by the Dark Energy Survey (DES) collaboration. Funding for the DES projects has been provided by the DOE, the NSF, the Ministry of Science and Education of Spain, the Science and Technology Facilities Council, UK, the Higher Education Funding Council for England, the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign, the Kavli Institute of Cosmological Physics at the University of Chicago, the Center for Cosmology and Astro-Particle Physics at Ohio State University, the Mitchell Institute for Fundamental Physics and Astronomy at Texas A&M University, the Funding Authority for Studies and Projects, Brazil, the Carlos Chagas Filho Foundation, Amparo, the Carlos Chagas Filho Foundation for Research Support in the State of Rio de Janeiro, the National Council for Scientific and Technological Development, Brazil, the Ministry of Science, Technology and Innovation, Brazil, the German Research Foundation, and the collaborating institutions in DES. The collaborating institutions are Argonne National Laboratory, the University of California at Santa Cruz, the University of Cambridge, the Centre for Energy, Environmental and Technological Research, Madrid, the University of Chicago, University College London, the DES-Brazil Consortium, the University of Edinburgh, the Eidgenossische Technische Hochschule (ETH) Zurich, the Fermi National Accelerator Laboratory, the University of Illinois at Urbana-Champaign, the Institute of Space Sciences of the Spanish National Research Council, the Institute for High Energy Physics, Spain, LBNL, the Ludwig Maximilian University of Munich and the associated Excellence Cluster Universe, the University of Michigan, NSF’s NOIRLab, the University of Nottingham, Ohio State University, the University of Pennsylvania, the University of Portsmouth, SLAC National Accelerator Laboratory, Stanford University, the University of Sussex, and Texas A&M University. BASS is a key project of the Telescope Access Program, which has been funded by the National Astronomical Observatories of China, the Chinese Academy of Sciences (the Strategic Priority Research Program the Emergence of Cosmological Structures, Grant No. XDB09000000) and the Special Fund for Astronomy from the Ministry of Finance. BASS is also supported by the External Cooperation Program of the Chinese Academy of Sciences (Grant No. 114A11KYSB20160057) and the Chinese National Natural Science Foundation (Grant Nos. 12120101003 and 11433005). The Legacy Survey team makes use of data products from the Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE), which is a project of the Jet Propulsion Laboratory/California Institute of Technology. NEOWISE is funded by NASA. The Legacy Surveys imaging of the Dark Energy Spectroscopic Instrument footprint is supported by the Director, Office of Science, Office of High Energy Physics of the DOE (Contract No. DE-AC02-05CH1123), by the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility under the same contract, and by the NSF, Division of Astronomical Sciences (Contract No. AST-0950945 to the National Optical Astronomy Observatory). This work made use of EveryStamp (https://tikk3r.github.io/EveryStamp/). This work made use of Astropy (http://www.astropy.org), a community-developed core Python package and an ecosystem of tools and resources for astronomy61,62,63.

Author information

Authors and Affiliations

Authors

Contributions

C.G. coordinated and wrote the paper, reduced the data and produced the LOFAR images. R.J.v.W. developed the self-calibration strategy and led the proposal that provided the data that this work is based on. E.O. worked on the initial calibration strategy for the decametre observations. F.d.G. developed some of the procedures used for this work. J.R.C provided scientific background information on the physics of radio emissions from stellar systems. W.L.W., J.R.C., H.J.A.R., M.B., G.B, G.K.M. and R.J.v.W. helped with writing the paper and provided feedback on the manuscript. A.B. performed the LoTSS target extraction. T.S. performed the LoTSS data reduction and survey management. F.S. had a critical role in developing the self-calibration software used in this work. J.M.G.H.J.d.J. developed the software required for managing the direction-dependent correction files. L.F.J. produced the cross-matched catalogues between this work and LoTSS. W.L.W., J.R.C and L.F.J. helped with the verification of the data products.

Corresponding author

Correspondence to C. Groeneveld.

Ethics declarations

Competing interests

The authors declare no competing interests.

Peer review

Peer review information

Nature Astronomy thanks the anonymous reviewer(s) for their contribution to the peer review of this work.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Supplementary Figs. 1–5 and Table 1.

Supplementary Data 1

Decameter catalogue.

Rights and permissions

Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Groeneveld, C., van Weeren, R.J., Osinga, E. et al. Characterization of the decametre sky at subarcminute resolution. Nat Astron 8, 786–795 (2024). https://doi.org/10.1038/s41550-024-02266-z

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/s41550-024-02266-z

Search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing