Journal Article2026

RGC: A radio AGN classifier based on deep learning

M. S. Hossain, M. S. H. Shahal, K. M. B. Asad, P. Saikia, A. Khan, F. Akter, A. A. Ali, M. A. Amin, D. P. Guha, M. Hasan, M. O. B. Jihad, A. Momen, S. Sen, A. K. M. M. Rahman

Astronomy & Astrophysics

EDP Sciences, Vol. 714, pp. A5, ISBN: 0004-6361

DOI: 10.1051/0004-6361/202557828Open AccessURL

Abstract

Context . Bent radio active galactic nuclei (RAGNs) – wide-angle tails (WATs) and narrow-angle tails (NATs) – trace dense environments in galaxy groups and clusters, yet no multi-class classifier simultaneously separates them from straight Fanaroff-Riley types (sFRI, sFRII) using visually inspected labels and unlabelled data. Aims . We release FIRST-2060, a four-class labelled dataset of 2060 RAGNs (sFRI, sFRII, WAT, NAT) constructed from three publicly available catalogues through multi-tier visual inspection, together with the semi-supervised RGC 1.0 model that leverages 20 000 unlabelled radio sources. We benchmarked RGC 1.0 against five supervised baselines spanning convolutional neural networks (CNNs) and vision transformers. Methods . FIRST-2060 is provided in two preprocessing variants: R L 1 , which retains spurious sources, and R L 2 , from which they are removed. The RGC model integrates the self-supervised framework Bootstrap Your Own Latent (BYOL) with an E (2)-equivariant steerable CNN (E2CNN) encoder, pre-trained on the unlabelled data and fine-tuned on the labelled sets. All six models were evaluated with five-fold cross-validation, gradient-weighted class activation mapping (Grad-CAM) attention analysis, and controlled class-imbalance experiments. Results . ConvNeXT ( M 1 ) and RGC ( M 2 ) form a top tier at macro- F 1 0.80 ± 0.02 and 0.79 ± 0.02, respectively, representing a difference within one standard deviation. The RGC model is the only model whose Grad-CAM contours consistently trace the morphological structure of RAGNs – lobes, jets, and bends – rather than defaulting to compact blobs or diffuse patterns. Conclusions . The four-class scheme introduced here enables WAT and NAT resolved catalogues that can serve as environment probes and progenitor classifications for diffuse cluster radio emission. The complementary strengths of M 1 and M 2 – in cross-type and within-type discrimination, respectively – suggest that an ensemble approach may offer a practical framework for survey-scale morphological catalogues.

Keywords

  • radio galaxy morphology
  • semi-supervised classification
  • multi-class classifier
  • radio galaxy environment

CCDS Authors

Prof. M Ashraful Amin, PhD
M Ashraful Amin, PhD

Prof. M Ashraful Amin, PhD

  • Founder Director, CCDS
  • Director, AI/ML, HCI & DS Wings

Published at

ACL, CHI, UbiComp, ECAI, WACV, PAKDD, IJCNN, ICPR, ICIP, HCII, CLEF, BLP, Scientific Reports, Pattern Recognition, JMIR, IEEE Access, Smart Agricultural Technology, Frontiers in Computational Neuroscience, Diabetes Research and Clinical Practice, PLOS ONE

References

  1. 1.Jia Deng, Wei Dong, Richard Socher, Li-Jia Li, Kai Li, Li Fei-Fei. (2009). ImageNet: A large-scale hierarchical image database. IEEE Computer Society Conference on Computer Vision and Pattern Recognition/Proceedings - IEEE Computer Society Conference on Computer Vision and Pattern Recognition/Proceedings, 248–255[10.1109/cvpr.2009.5206848]
  2. 2.Zhou Wang, A.C. Bovik, H.R. Sheikh, E.P. Simoncelli. (2004). Image quality assessment: from error visibility to structural similarity. IEEE Transactions on Image Processing, 13(4), 600–612[10.1109/tip.2003.819861]
  3. 3.Ramprasaath R. Selvaraju, Michael Cogswell, Abhishek Das, Ramakrishna Vedantam, Devi Parikh, Dhruv Batra. (2017). Grad-CAM: Visual Explanations from Deep Networks via Gradient-Based Localization. IEEE/CVF International Conference on Computer Vision (ICCV), 618–626[10.1109/iccv.2017.74]
  4. 4.R. D. Blandford, R. L. Znajek. (1977). Electromagnetic extraction of energy from Kerr black holes. Monthly Notices of the Royal Astronomical Society, 179(3), 433–456[10.1093/mnras/179.3.433]
  5. 5.C. Megan Urry, Paolo Padovani. (1995). Unified Schemes for Radio-Loud Active Galactic Nuclei. Publications of the Astronomical Society of the Pacific, 107, 803[10.1086/133630]
  6. 6.Robert H. Becker, Richard L. White, David J. Helfand. (1995). The FIRST Survey: Faint Images of the Radio Sky at Twenty Centimeters. The Astrophysical Journal, 450, 559[10.1086/176166]
  7. 7.B. L. Fanaroff, J. M. Riley. (1974). The Morphology of Extragalactic Radio Sources of High and Low Luminosity. Monthly Notices of the Royal Astronomical Society, 167(1), 31P–36P[10.1093/mnras/167.1.31p]
  8. 8.Amy Brand, Liz Allen, Micah Altman, Marjorie Hlava, Jo Scott. (2015). Beyond authorship: attribution, contribution, collaboration, and credit. Learned Publishing, 28(2), 151–155[10.1087/20150211]
  9. 9.R. J. van Weeren, F. de Gasperin, H. Akamatsu, M. Brüggen, L. Feretti, H. Kang, A. Stroe, F. Zandanel. (2019). Diffuse Radio Emission from Galaxy Clusters. Space Science Reviews, 215(1)[10.1007/s11214-019-0584-z]
  10. 10.T. W. Shimwell, M. J. Hardcastle, C. Tasse, P. N. Best, H. J. A. Röttgering, W. L. Williams, A. Botteon, A. Drabent, A. Mechev, A. Shulevski, R. J. van Weeren, L. Bester, M. Brüggen, G. Brunetti, J. R. Callingham, K. T. Chyży, J. E. Conway, T. J. Dijkema, K. Duncan, F. de Gasperin, C. L. Hale, M. Haverkorn, B. Hugo, N. Jackson, M. Mevius, G. K. Miley, L. K. Morabito, R. Morganti, A. Offringa, J. B. R. Oonk, D. Rafferty, J. Sabater, D. J. B. Smith, D. J. Schwarz, O. Smirnov, S. P. O’Sullivan, H. Vedantham, G. J. White, J. G. Albert, L. Alegre, B. Asabere, D. J. Bacon, A. Bonafede, E. Bonnassieux, M. Brienza, M. Bilicki, M. Bonato, G. Calistro Rivera, R. Cassano, R. Cochrane, J. H. Croston, V. Cuciti, D. Dallacasa, A. Danezi, R. J. Dettmar, G. Di Gennaro, H. W. Edler, T. A. Enßlin, K. L. Emig, T. M. O. Franzen, C. García-Vergara, Y. G. Grange, G. Gürkan, M. Hajduk, G. Heald, V. Heesen, D. N. Hoang, M. Hoeft, C. Horellou, M. Iacobelli, M. Jamrozy, V. Jelić, R. Kondapally, P. Kukreti, M. Kunert-Bajraszewska, M. Magliocchetti, V. Mahatma, K. Małek, S. Mandal, F. Massaro, Z. Meyer-Zhao, B. Mingo, R. I. J. Mostert, D. G. Nair, S. J. Nakoneczny, B. Nikiel-Wroczyński, E. Orrú, U. Pajdosz-Śmierciak, T. Pasini, I. Prandoni, H. E. van Piggelen, K. Rajpurohit, E. Retana-Montenegro, C. J. Riseley, A. Rowlinson, A. Saxena, C. Schrijvers, F. Sweijen, T. M. Siewert, R. Timmerman. (2022). The LOFAR Two-metre Sky Survey. Astronomy and Astrophysics, 659, A1[10.1051/0004-6361/202142484]
  11. 11.M. J. Hardcastle, D. A. Evans, J. H. Croston. (2007). Hot and cold gas accretion and feedback in radio-loud active galaxies. Monthly Notices of the Royal Astronomical Society, 376(4), 1849–1856[10.1111/j.1365-2966.2007.11572.x]
  12. 12.B Mingo, J H Croston, M J Hardcastle, P N Best, K J Duncan, R Morganti, H J A Rottgering, J Sabater, T W Shimwell, W L Williams, M Brienza, G Gurkan, V H Mahatma, L K Morabito, I Prandoni, M Bondi, J Ineson, S Mooney. (2019). Revisiting the Fanaroff–Riley dichotomy and radio-galaxy morphology with the LOFAR Two-Metre Sky Survey (LoTSS). Monthly Notices of the Royal Astronomical Society, 488(2), 2701–2721[10.1093/mnras/stz1901]
  13. 13.A. K. Aniyan, K. Thorat. (2017). Classifying Radio Galaxies with the Convolutional Neural Network. The Astrophysical Journal Supplement Series, 230(2), 20[10.3847/1538-4365/aa7333]
  14. 14.Frazer N. Owen, Lawrence Rudnick. (1976). Radio Sources with Wide-Angle Tails in Abell Clusters of Galaxies. The Astrophysical Journal, 205, L1[10.1086/182077]
  15. 15.J. K. Banfield, O. I. Wong, K. W. Willett, R. P. Norris, L. Rudnick, S. S. Shabala, B. D. Simmons, C. Snyder, A. Garon, N. Seymour, E. Middelberg, H. Andernach, C. J. Lintott, K. Jacob, A. D. Kapińska, M. Y. Mao, K. L. Masters, M. J. Jarvis, K. Schawinski, E. Paget, R. Simpson, H.-R. Klöckner, S. Bamford, T. Burchell, K. E. Chow, G. Cotter, L. Fortson, I. Heywood, T. W. Jones, S. Kaviraj, Á. R. López-Sánchez, W. P. Maksym, K. Polsterer, K. Borden, R. P. Hollow, L. Whyte. (2015). Radio Galaxy Zoo: host galaxies and radio morphologies derived from visual inspection. Monthly Notices of the Royal Astronomical Society, 453(3), 2327–2341[10.1093/mnras/stv1688]
  16. 16.Francesco de Gasperin, Huib T. Intema, Timothy W. Shimwell, Gianfranco Brunetti, Marcus Brüggen, Torsten A. Enßlin, Reinout J. van Weeren, Annalisa Bonafede, Huub J. A. Röttgering. (2017). Gentle reenergization of electrons in merging galaxy clusters. Science Advances, 3(10), e1701634[10.1126/sciadv.1701634]
  17. 17.Chen Wu, Oiwei Ivy Wong, Lawrence Rudnick, Stanislav S Shabala, Matthew J Alger, Julie K Banfield, Cheng Soon Ong, Sarah V White, Avery F Garon, Ray P Norris, Heinz Andernach, Jean Tate, Vesna Lukic, Hongming Tang, Kevin Schawinski, Foivos I Diakogiannis. (2018). Radio Galaxy Zoo: Claran – a deep learning classifier for radio morphologies. Monthly Notices of the Royal Astronomical Society, 482(1), 1211–1230[10.1093/mnras/sty2646]
  18. 18.D. D. Proctor. (2011). MORPHOLOGICAL ANNOTATIONS FOR GROUPS IN THE FIRST DATABASE. The Astrophysical Journal Supplement Series, 194(2), 31[10.1088/0067-0049/194/2/31]
  19. 19.Christopher P. O’Dea, Stefi A. Baum. (2023). Wide-Angle-Tail (WAT) Radio Sources. Galaxies, 11(3), 67[10.3390/galaxies11030067]
  20. 20.G. K. MILEY, G. C. PEROLA, P. C. VAN DER KRUIT, H. VAN DER LAAN. (1972). Active Galaxies with Radio Trails in Clusters. Nature, 237(5353), 269–272[10.1038/237269a0]
  21. 21.V Lukic, M Brüggen, J K Banfield, O I Wong, L Rudnick, R P Norris, B Simmons. (2018). Radio Galaxy Zoo: compact and extended radio source classification with deep learning. Monthly Notices of the Royal Astronomical Society, 476(1), 246–260[10.1093/mnras/sty163]
  22. 22.L. Rudnick, F. N. Owen. (1976). Head-tail radio sources in clusters of galaxies. The Astrophysical Journal, 203, L107[10.1086/182030]
  23. 23.S. Mandal, H. T. Intema, R. J. van Weeren, T. W. Shimwell, A. Botteon, G. Brunetti, F. de Gasperin, M. Brüggen, G. Di Gennaro, R. Kraft, H. J. A. Röttgering, M. Hardcastle, C. Tasse. (2019). Revived fossil plasma sources in galaxy clusters. Astronomy and Astrophysics, 634, A4[10.1051/0004-6361/201936560]
  24. 24.Avery F. Garon, Lawrence Rudnick, O. Ivy Wong, Tom W. Jones, Jin-Ah Kim, Heinz Andernach, Stanislav S. Shabala, Anna D. Kapińska, Ray P. Norris, Francesco de Gasperin, Jean Tate, Hongming Tang. (2019). Radio Galaxy Zoo: The Distortion of Radio Galaxies by Galaxy Clusters. The Astronomical Journal, 157(3), 126[10.3847/1538-3881/aaff62]
  25. 25.T J Galvin, M T Huynh, R P Norris, X R Wang, E Hopkins, K Polsterer, N O Ralph, A N O’Brien, G H Heald. (2020). Cataloguing the radio-sky with unsupervised machine learning: a new approach for the SKA era. Monthly Notices of the Royal Astronomical Society, 497(3), 2730–2758[10.1093/mnras/staa1890]
  26. 26.Anna M M Scaife, Fiona Porter. (2021). Fanaroff–Riley classification of radio galaxies using group-equivariant convolutional neural networks. Monthly Notices of the Royal Astronomical Society, 503(2), 2369–2379[10.1093/mnras/stab530]
  27. 27.Inigo V Slijepcevic, Anna M M Scaife, Mike Walmsley, Micah Bowles, O Ivy Wong, Stanislav S Shabala, Hongming Tang. (2022). Radio Galaxy Zoo: using semi-supervised learning to leverage large unlabelled data sets for radio galaxy classification under data set shift. Monthly Notices of the Royal Astronomical Society, 514(2), 2599–2613[10.1093/mnras/stac1135]
  28. 28.S. Dehghan, M. Johnston-Hollitt, T. M. O. Franzen, R. P. Norris, N. A. Miller. (2014). BENT-TAILED RADIO SOURCES IN THE AUSTRALIA TELESCOPE LARGE AREA SURVEY OF THE CHANDRA DEEP FIELD SOUTH. The Astronomical Journal, 148(5), 75[10.1088/0004-6256/148/5/75]
  29. 29.Viera Maslej-Krešňáková, Khadija El Bouchefry, Peter Butka. (2021). Morphological classification of compact and extended radio galaxies using convolutional neural networks and data augmentation techniques. Monthly Notices of the Royal Astronomical Society, 505(1), 1464–1475[10.1093/mnras/stab1400]
  30. 30.Inigo V Slijepcevic, Anna M M Scaife, Mike Walmsley, Micah Bowles, O Ivy Wong, Stanislav S Shabala, Sarah V White. (2023). Radio galaxy zoo: towards building the first multipurpose foundation model for radio astronomy with self-supervised learning. RAS Techniques and Instruments, 3(1), 19–32[10.1093/rasti/rzad055]
  31. 31.Tapan K. Sasmal, Soumen Bera, Sabyasachi Pal, Soumen Mondal. (2022). A New Catalog of Head–Tail Radio Galaxies from the VLA FIRST Survey. The Astrophysical Journal Supplement Series, 259(2), 31[10.3847/1538-4365/ac4473]
  32. 32.Steven Ndung’u, Trienko Grobler, Stefan J. Wijnholds, Dimka Karastoyanova, George Azzopardi. (2023). Advances on the morphological classification of radio galaxies: A review. New Astronomy Reviews, 97, 101685[10.1016/j.newar.2023.101685]
  33. 33.Fiona A M Porter, Anna M M Scaife. (2023). MiraBest: a data set of morphologically classified radio galaxies for machine learning. RAS Techniques and Instruments, 2(1), 293–306[10.1093/rasti/rzad017]
  34. 34.Franco Vazza, Andrea Botteon. (2024). The Seeding of Cosmic Ray Electrons by Cluster Radio Galaxies: A Review. Galaxies, 12(2), 19[10.3390/galaxies12020019]
  35. 35.Netai Bhukta, Sushanta K Mondal, Sabyasachi Pal. (2022). Tailed radio galaxies from the TIFR GMRT sky survey. Monthly Notices of the Royal Astronomical Society, 516(1), 372–390[10.1093/mnras/stac2001]
  36. 36.O Ivy Wong, A F Garon, M J Alger, L Rudnick, S S Shabala, K W Willett, J K Banfield, H Andernach, R P Norris, J Swan, M J Hardcastle, C J Lintott, S V White, N Seymour, A D Kapińska, H Tang, B D Simmons, K Schawinski. (2024). Radio Galaxy Zoo data release 1: 100185 radio source classifications from the FIRST and ATLAS surveys. Monthly Notices of the Royal Astronomical Society, 536(4), 3488–3506[10.1093/mnras/stae2790]
  37. 37.Baoqiang Lao, Heinz Andernach, Xiaolong Yang, Xiang Zhang, Rushuang Zhao, Zhen Zhao, Yun Yu, Xiaohui Sun, Sheng-Li Qin. (2025). Identification of 4876 Bent-tail Radio Galaxies in the FIRST Survey Using Deep Learning Combined with Visual Inspection. The Astrophysical Journal Supplement Series, 276(2), 46[10.3847/1538-4365/ad9c6d]
  38. 38.Jack O. Burns. (1998). Stormy Weather in Galaxy Clusters. Science, 280(5362), 400–404[10.1126/science.280.5362.400]
  39. 39.Emmet Golden-Marx, E. L. Blanton, R. Paterno-Mahler, M. Brodwin, M. L. N. Ashby, E. Moravec, L. Shen, B. C. Lemaux, L. M. Lubin, R. R. Gal, A. R. Tomczak. (2021). The High-redshift Clusters Occupied by Bent Radio AGN (COBRA) Survey: Radio Source Properties. The Astrophysical Journal, 907(2), 65[10.3847/1538-4357/abcd96]
  40. 40.Sabyasachi Pal, Shobha Kumari. (2023). A new catalog of head–tail radio galaxies from LoTSS DR1. Journal of Astrophysics and Astronomy, 44(1)[10.1007/s12036-022-09892-x]
  41. 41.Emmet Golden-Marx, E. Moravec, L. Shen, Z. Cai, E. L. Blanton, M. L. Gendron-Marsolais, H. J. A. Röttgering, R. J. van Weeren, V. Buiten, R. D. P. Grumitt, J. Golden-Marx, S. Pinjarkar, H. Tang. (2023). The High-redshift Clusters Occupied by Bent Radio AGN (COBRA) Survey: Investigating the Role of Environment on Bent Radio AGNs Using LOFAR. The Astrophysical Journal, 956(2), 87[10.3847/1538-4357/acf46b]
  42. 42.Nicolas Baron Perez, Marcus Brüggen, Gregor Kasieczka, Luisa Lucie-Smith. (2025). Classification of radio sources through self-supervised learning. Astronomy and Astrophysics, 699, A302[10.1051/0004-6361/202554735]
  43. 43.E. Vardoulaki, V. Backöfer, A. Finoguenov, F. Vazza, J. Comparat, G. Gozaliasl, I. H. Whittam, C. L. Hale, J. R. Weaver, A. M. Koekemoer, J. D. Collier, B. Frank, I. Heywood, S. Sekhar, A. R. Taylor, S. Pinjarkar, M. J. Hardcastle, T. Shimwell, M. Hoeft, S. V. White, F. An, F. Tabatabaei, Z. Randriamanakoto, M. D. Filipovic. (2025). The jet paths of radio active galactic nuclei and their cluster weather. Astronomy and Astrophysics, 695, A178[10.1051/0004-6361/202453180]
  44. 44.Ray P. Norris, Joshua Marvil, J. D. Collier, Anna D. Kapińska, Andrew N. O’Brien, L. Rudnick, Heinz Andernach, Jacobo Asorey, Michael J. I. Brown, Marcus Brüggen, Evan Crawford, Jayanne English, Syed Faisal ur Rahman, Miroslav D. Filipović, Yjan Gordon, Gülay Gürkan, Catherine Hale, Andrew M. Hopkins, Minh T. Huynh, Kim HyeongHan, M. James Jee, Bärbel S. Koribalski, Emil Lenc, Kieran Luken, David Parkinson, Isabella Prandoni, Wasim Raja, Thomas H. Reiprich, Christopher J. Riseley, Stanislav S. Shabala, Jaimie R. Sheil, Tessa Vernstrom, Matthew T. Whiting, James R. Allison, C. S. Anderson, Lewis Ball, Martin Bell, John Bunton, T. J. Galvin, Neeraj Gupta, Aidan Hotan, Colin Jacka, Peter J. Macgregor, Elizabeth K. Mahony, Umberto Maio, Vanessa Moss, M. Pandey-Pommier, Maxim A. Voronkov. (2021). The Evolutionary Map of the Universe pilot survey. Publications of the Astronomical Society of Australia, 38[10.1017/pasa.2021.42]
  45. 45.Mir Sazzat Hossain, Sugandha Roy, K.M.B. Asad, Arshad Momen, Amin Ahsan Ali, M Ashraful Amin, A. K. M. Mahbubur Rahman. (2023). Morphological classification of Radio Galaxies using Semi-Supervised Group Equivariant CNNs. Procedia Computer Science, 222, 601–612[10.1016/j.procs.2023.08.198]
  46. 46.S. van der Jagt, E. Osinga, R. J. van Weeren, G. K. Miley, I. D. Roberts, A. Botteon, A. Ignesti. (2025). The phase-space of tailed radio galaxies in massive clusters. Astronomy and Astrophysics, 699, A66[10.1051/0004-6361/202451216]
  47. 47.R.C. Kapoor. (2023). COMET 1P/HALLEY IN 1910: TALES FROM INDIA. Journal of Astronomical History and Heritage, 26(2), 411–440[10.3724/sp.j.1440-2807.2023.06.36]
  48. 48.Mir Sazzat Hossain, Khan Muhammad Bin Asad, Payaswini Saikia, Adrita Khan, Md Akil Raihan Iftee, Rakibul Hasan Rajib, Arshad Momen, Md Ashraful Amin, Amin Ahsan Ali, AKM Mahbubur Rahman. (2025). RGC-Bent: A Novel Dataset for Bent Radio Galaxy Classification. Proceedings - International Conference on Image Processing, 2868–2873[10.1109/icip55913.2025.11084387]
← All publications