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

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 (EW 0 &gt; 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 II λ 4687 /H β = 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 ]/H β vs [N II ]/H α ) 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.

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Publication Details

Journal
Astronomy and Astrophysics
Published
2024-11-21
DOI
https://doi.org/10.1051/0004-6361/202451551
Citations
19
Primary Topic
Astronomy and Astrophysical Research
Type
article
Field-Weighted Citation Impact
9.62

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article

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

Xuheng Ding, Zhaoxuan Liu, N. M. Förster-Schreiber, M. Boquien et al.
19 citations
Astronomy and Astrophysics
Astronomy and Astrophysical Research
9.62
article

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

Xuheng Ding, Zhaoxuan Liu, N. M. Förster-Schreiber, M. Boquien, Ilse De Looze, M. Ginolfi, M. Relaño, J. González-López, S. Bovino, Patrick Ogle, Francesca Pozzi, Dominik A. Riechers, Roberto J. Assef, Nimish P. Hathi, D. Liu, M. Solimano, Vicente Villanueva, G. Zamorani, Anton M. Koekemoer, Rodrigo Herrera-Camus, Gareth C. Jones, Hanae Inami, L. Vallini, A. Ferrara, D. Vergani, Belén Alcalde Pampliega, Caitlin M. Casey, K. Telikova, M. Béthermin, C. Gruppioni, Nikolaus Sulzenauer, S. Fujimoto, Justin Spilker, L. Lee, S. Veilleux, R. L. Davies, Ana Posses, Elisabete da Cunha, Manuel Aravena, Juno Li, L. Guaita, Andreas L. Faisst, T. Díaz-Santos, Wenxin Wang, P. Cassata, L. Yan, E. Ibar, M. Romano, Donald B. Fisher, J. Molina, K. G. C. Vasan
article en
19 citations

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 (EW 0 &gt; 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 II λ 4687 /H β = 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 ]/H β vs [N II ]/H α ) 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.

Astronomy and AstrophysicsVol. 693
National Aeronautics and Space Administration, Space Telescope Science Institute, Australian Government, European Commission, Agence Nationale de la Recherche, Fundacja na rzecz Nauki Polskiej, Narodowe Centrum Nauki, Agencia Nacional de Investigación y Desarrollo, Australian Research Council, Japan Society for the Promotion of Science
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Astronomy and Astrophysical Research
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