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UNCOVER: A NIRSpec Identification of a Broad-line AGN at z = 8.50

Kokorev, V, Fujimoto, S, Labbe, I, Greene, JE, Bezanson, R, Dayal, P, Nelson, EJ, Atek, H, Brammer, G, Caputi, KI, Chemerynska, I, Cutler, SE, Feldmann, R, Fudamoto, Y, Furtak, LJ, Goulding, AD, de Graaff, A, Leja, J, Marchesini, D, Miller, TB , Nanayakkara, T, Oesch, PA, Pan, R, Price, SH, Setton, DJ, Smit, R, Stefanon, M, Wang, B, Weaver, JR, Whitaker, KE, Williams, CC and Zitrin, A (2023) UNCOVER: A NIRSpec Identification of a Broad-line AGN at z = 8.50. Astrophysical Journal Letters, 957 (1). ISSN 2041-8205

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Deep observations with the James Webb Space Telescope (JWST) have revealed an emerging population of red pointlike sources that could provide a link between the postulated supermassive black hole seeds and observed quasars. In this work, we present a JWST/NIRSpec spectrum from the JWST Cycle 1 UNCOVER Treasury survey of a massive accreting black hole at z = 8.50 displaying a clear broad-line component as inferred from the Hβ line with FWHM = 3439 ± 413 km s−1, typical of the broad-line region of an active galactic nucleus (AGN). The AGN nature of this object is further supported by high ionization, as inferred from emission lines, and a point-source morphology. We compute a black hole mass of log 10 ( M BH / M ⊙ ) = 8.17 ± 0.42 and a bolometric luminosity of L bol ∼ 6.6 × 1045 erg s−1. These values imply that our object is accreting at ∼40% of the Eddington limit. Detailed modeling of the spectral energy distribution in the optical and near-infrared, together with constraints from ALMA, indicate an upper limit on the stellar mass of log 10 ( M * / M ⊙ ) < 8.7 , which would lead to an unprecedented ratio of black hole to host mass of at least ∼30%. This is orders of magnitude higher compared to the local QSOs but consistent with recent AGN studies at high redshift with JWST. This finding suggests that a nonnegligible fraction of supermassive black holes either started out from massive seeds and/or grew at a super-Eddington rate at high redshift. Given the predicted number densities of high-z faint AGN, future NIRSpec observations of larger samples will allow us to further investigate galaxy-black hole coevolution in the early Universe.

Item Type: Article
Uncontrolled Keywords: 0201 Astronomical and Space Sciences; Astronomy & Astrophysics
Subjects: Q Science > QB Astronomy
Divisions: Astrophysics Research Institute
Publisher: American Astronomical Society
SWORD Depositor: A Symplectic
Date Deposited: 11 Dec 2023 16:29
Last Modified: 11 Dec 2023 16:30
DOI or ID number: 10.3847/2041-8213/ad037a
URI: https://researchonline.ljmu.ac.uk/id/eprint/22080
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