A hidden active galactic nucleus powering bright [O III] nebulae in a protocluster at z = 4.5 revealed by JWST

Creators: Solimano, M.¹; González-López, J.^{2, 3}; Aravena, M.¹; Alcalde Pampliega, B.^{1, 4}; Assef, R. J.¹; Béthermin, M.^{5, 6}; Boquien, M.⁷; Bovino, S.^{8, 9, 10}; Casey, C. M.^{11, 12}; Cassata, P.^{13, 14}; da Cunha, E.¹⁵; Davies, R. L.^{16, 17}; De Looze, I.^{18, 19}; Ding, X.²⁰; Díaz-Santos, T.²¹; Faisst, A. L.^{22, 23}; Ferrara, A.²⁴; Fisher, D. B.^{16, 17}; Förster-Schreiber, N. M.²⁵; Fujimoto, S.¹¹; Ginolfi, M.^{26, 10}; Gruppioni, C.²⁷; Guaita, L.²⁸; Hathi, N.²⁹; Herrera-Camus, R.⁸; Ibar, E.³⁰; Inami, H.³¹; Jones, G. C.²⁵; Koekemoer, A. M.²⁹; Lee, L. L.³²; Li, J.¹⁵; Liu, D.³³; Liu, Z.^{20, 34}; Molina, J.³⁰; Ogle, P.²⁹; Posses, A. C.¹; Pozzi, F.³⁴; Relaño, M.³⁵; Riechers, D. A.³⁶; Romano, M.^{37, 14, 38}; Spilker, J.³⁹; Sulzenauer, N.³⁷; Telikova, K.¹; Vallini, L.²⁷; Vasan, K. G. C.⁴⁰; Veilleux, S.⁴¹; Vergani, D.²⁷; Villanueva, V.⁸; Wang, W.⁴²; Yan, L.²³; Zamorani, G.²⁷

1. Diego Portales University
2. Pontificia Universidad Católica de Chile
3. Las Campanas Observatory
4. European Southern Observatory
5. Observatory of Strasbourg
6. Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
7. Lagrange Laboratory
8. University of Concepción
9. Sapienza University of Rome
10. Arcetri Astrophysical Observatory
11. The University of Texas at Austin
12. University of Copenhagen
13. University of Padua
14. Osservatorio Astronomico di Padova
15. International Centre for Radio Astronomy Research
16. Swinburne University of Technology
17. Centre of Excellence for All-Sky Astrophysics
18. Ghent University
19. University College London
20. Kavli Institute for the Physics and Mathematics of the Universe
21. National Astronomical Observatories
22. Infrared Processing and Analysis Center
23. California Institute of Technology
24. Scuola Normale Superiore di Pisa
25. University of Oxford
26. University of Florence
27. Osservatorio di Astrofisica e Scienza dello Spazio
28. Andrés Bello University
29. Space Telescope Science Institute
30. University of Valparaíso
31. Hiroshima University
32. Max Planck Institute for Extraterrestrial Physics
33. Purple Mountain Observatory
34. University of Tokyo
35. University of Granada
36. University of Cologne
37. Max Planck Institute for Radio Astronomy
38. National Centre for Nuclear Research
39. Texas A&M University
40. University of California, Davis
41. University of Maryland, College Park
42. Heidelberg University

Abstract

Galaxy protoclusters are sites of rapid growth, with a high density of massive galaxies driving elevated rates of star formation and accretion onto supermassive black holes. Here, we present new JWST/NIRSpec IFU observations of the J1000+0234 group at z = 4.54, a dense region of a protocluster hosting a massive, dusty star forming galaxy (DSFG). The new data reveal two extended, high-equivalent-width (EW₀ > 1000 Å) [O III] nebulae that appear at both sides of the DSFG along its minor axis (namely O3-N and O3-S). On one hand, the spectrum of O3-N shows a broad and blueshifted component with a full width at half maximum (FWHM) of ∼1300 km s⁻¹, suggesting an outflow origin. On the other hand, O3-S stretches over 8.6 kpc, and has a velocity gradient that spans 800 km s⁻¹, but shows no evidence of a broad component. However, both sources seem to be powered at least partially by an active galactic nucleus (AGN), so we classified them as extended emission-line regions (EELRs). The strongest evidence comes from the detection of the high-ionization [Ne V] λ 3427 line toward O3-N, which paired with the lack of hard X-rays implies an obscuring column density above the Compton-thick regime. The [Ne V] line is not detected in O3-S, but we measure a He IIλ 4687 /Hβ = 0.25, which is well above the expectation for star formation. Despite the remarkable alignment of O3-N and O3-S with two radio sources, we do not find evidence of shocks from a radio jet that could be powering the EELRs. We interpret this as O3-S being externally irradiated by the AGN, akin to the famous Hanny’s Voorwerp object in the local Universe. In addition, more classical line ratio diagnostics (e.g., [O III]/Hβ vs [N II]/Hα) put the DSFG itself in the AGN region of the diagrams, and therefore suggest it to be the most probable AGN host. These results showcase the ability of JWST to unveil obscured AGN at high redshifts.

Copyright and License

Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Acknowledgement

This work is based in part on observations made with the NASA/ESA/CSA James Webb Space Telescope. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST. These observations are associated with programs JWST-GO-01727, JWST-GO-0345, and JWST-GO-04265. We also thank Mingyu Li for useful discussions and the My Filter tool https://doi.org/10.5281/zenodo.10210201. M. S. was financially supported by Becas-ANID scholarship #21221511. M. S., S. B., M. A., R. J. A., J. G-L., M. Boquien, and V. V. all acknowledge support from ANID BASAL project FB210003. M. R. acknowledges support from the Narodowe Centrum Nauki (UMO-2020/38/E/ST9/00077) and support from the Foundation for Polish Science (FNP) under the program START 063.2023. E. I. acknowledges funding by ANID FONDECYT Regular 1221846. M. Boquien gratefully acknowledges support from the FONDECYT regular grant 1211000. This work was supported by the French government through the France 2030 investment plan managed by the National Research Agency (ANR), as part of the Initiative of Excellence of Université Côte d’Azur under reference number ANR-15-IDEX-01. G. C. J. acknowledges funding from the “FirstGalaxies” Advanced Grant from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant agreement No. 78905). R. J. A. was supported by FONDECYT grant number 1231718. H.I. acknowledges support from JSPS KAKENHI Grant Number JP21H01129 and the Ito Foundation for Promotion of Science. R. L. D is supported by the Australian Research Council through the Discovery Early Career Researcher Award (DECRA) Fellowship DE240100136 funded by the Australian Government.

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A hidden active galactic nucleus powering bright [O III] nebulae in a protocluster at z = 4.5 revealed by JWST