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

**Authors:** Vasily Kokorev, Seiji Fujimoto, Ivo Labbe, Jenny E. Greene, Rachel Bezanson, Pratika Dayal, Erica J. Nelson, Hakim Atek, Gabriel Brammer, 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  
**arXiv:** [2308.11610](https://arxiv.org/abs/2308.11610)  
**Date:** 2023-08-22  
**Summary page:** https://www.summarizepaper.com/en/paper/2308.11610v1/

## Key points

- Deep observations with the James Webb Space Telescope (JWST) have found red point-like sources
- These sources could bridge the gap between supermassive black hole seeds and observed quasars
- A JWST/NIRSpec spectrum from the Cycle 1 UNCOVER Treasury survey reveals a massive accreting black hole at a redshift of $z=8.50$
- The spectrum shows a clear broad-line component, specifically inferred from the H$\beta$ line, indicating an active galactic nucleus (AGN)
- High ionization levels inferred from emission lines and point-source morphology further support the AGN nature of this object
- Black hole mass is calculated to be log$_{10}(M_{\rm BH}/M_\odot)=8.17\pm0.42$, with a bolometric luminosity of $L_{\rm bol}\sim6.6\times10^{45}$ erg s$^{-1}$
- The object is accreting at approximately 40% of its Eddington limit
- Modeling suggests an upper limit on stellar mass of log$_{10}(M_{\rm *}/M_\odot)<8.7$, implying a black hole to host mass ratio exceeding 30%
- This discovery aligns with recent AGN studies using JWST and suggests that many supermassive black holes may have originated from massive seeds or experienced super-Eddington accretion rates in the early universe
- Future observations using JWST's NIRSpec instrument will enable further investigations into coevolution between galaxies and black holes in the early universe

## Summary

The Deep observations with the James Webb Space Telescope (JWST) have uncovered a population of red point-like sources that could bridge the gap between supermassive black hole seeds and observed quasars. In this study, the researchers present a JWST/NIRSpec spectrum from the JWST Cycle 1 UNCOVER Treasury survey, focusing on a massive accreting black hole at a redshift of $z=8.50$. The spectrum reveals a clear broad-line component, specifically inferred from the H$\beta$ line with a full width at half maximum (FWHM) of $3439\pm413$ km s$^{-1}$, which is characteristic of the broad line region of an active galactic nucleus (AGN). The AGN nature of this object is further supported by high ionization levels inferred from emission lines and its point-source morphology. The researchers calculate the black hole mass to be log$_{10}(M_{\rm BH}/M_\odot)=8.17\pm0.42$, along with a bolometric luminosity of $L_{\rm bol}\sim6.6\times10^{45}$ erg s$^{-1}$. These values indicate that the object is accreting at approximately 40% of its Eddington limit. Detailed modeling of the spectral energy distribution in the optical and near-infrared combined with constraints from ALMA observations suggests an upper limit on the stellar mass of log$_{10}(M_{\rm *}/M_\odot)<8.7$. This implies an unprecedented ratio of black hole to host mass exceeding 30%. This discovery aligns with recent AGN studies at high redshift using JWST and suggests that a significant fraction of supermassive black holes may have originated from massive seeds or experienced super-Eddington accretion rates in the early universe. With its predicted number densities for high-redshift faint AGN, future observations using JWST's NIRSpec instrument will enable further investigations into coevolution between galaxies and black holes in the early universe.