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

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arxiv 2308.11610 v4 pith:7AHJSDW3 submitted 2023-08-22 astro-ph.GA

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

Vasily Kokorev , Seiji Fujimoto , Ivo Labbe , Jenny E. Greene , Rachel Bezanson , Pratika Dayal , Erica J. Nelson , Hakim Atek
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Gabriel Brammer Karina I. Caputi Iryna Chemerynska Sam E. Cutler Robert Feldmann Yoshinobu Fudamoto Lukas J. Furtak Andy D. Goulding Anna de Graaff Joel Leja Danilo Marchesini Tim B. Miller Themiya Nanayakkara Pascal Oesch Richard Pan Sedona H. Price David J. Setton Renske Smit Mauro Stefanon Bingjie Wang John R. Weaver Katherine E. Whitaker Christina C. Williams Adi Zitrin
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keywords blackholejwsthighlinemassnirspecaccreting
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Deep observations with JWST have revealed an emerging population of red point-like 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 H$\beta$ line with FWHM = $3439\pm413$ 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 the black hole mass of log$_{10}(M_{\rm BH}/M_\odot)=8.17\pm0.42$, and a bolometric luminosity of $L_{\rm bol}\sim6.6\times10^{45}$ erg s$^{-1}$. These values imply that our object is accreting at $\sim 40\%$ 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$_{10}(M_{\rm *}/M_\odot)<8.7$, which would lead to an unprecedented ratio of black hole to host mass of at least $\sim 30 \%$. This is orders of magnitude higher compared to the local QSOs, but is consistent with recent AGN studies at high redshift with JWST. This finding suggests that a non-negligible 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 the galaxy-black hole co-evolution in the early Universe.

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Cited by 6 Pith papers

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