A CEERS Discovery of an Accreting Supermassive Black Hole 570 Myr after the Big Bang: Identifying a Progenitor of Massive z > 6 Quasars

TL;DR

This work reports the first actively accreting supermassive black hole at $z=8.679$ in CEERS_1019, identified with JWST NIRSpec and imaging data. A broad $\mathrm{H}\beta$ line reveals a BH of $\log (M_{\mathrm{BH}}/M_{\odot}) = 6.95 \pm 0.37$ accreting at $\lambda_{\mathrm{Edd}} \approx 1.3 \pm 0.5$, while the host galaxy has $\log (M_{*}/M_{\odot}) \approx 9.5$, SFR $\sim 30\,M_{\odot}\,\mathrm{yr^{-1}}$, and sub-solar metallicity ($Z/Z_{\odot} \approx 0.095$). Nebular diagnostics indicate dense, highly ionized gas with $n_{\mathrm{e}} \sim 2\times 10^{3}\ \mathrm{cm}^{-3}$ and $T_{\mathrm{e}} \approx 1.86\times 10^{4}$ K, though the high ionization could arise from either star formation or AGN activity. Theoretical implications favor either direct-collapse seeds with near-Eddington growth or stellar seeds undergoing episodic super-Eddington accretion, offering crucial constraints on SMBH seeding and early BH–galaxy co-evolution, and suggesting a role for AGN in ionizing their environment during reionization in overdense regions.

Abstract

We report the discovery of an accreting supermassive black hole at z=8.679, in CEERS_1019, a galaxy previously discovered via a Ly$α$-break by Hubble and with a Ly$α$ redshift from Keck. As part of the Cosmic Evolution Early Release Science (CEERS) survey, we observed this source with JWST/NIRSpec spectroscopy, MIRI and NIRCam imaging, and NIRCam/WFSS slitless spectroscopy. The NIRSpec spectra uncover many emission lines, and the strong [O III] emission line confirms the ground-based Ly$α$ redshift. We detect a significant broad (FWHM~1200 km/s) component in the H$β$ emission line, which we conclude originates in the broad-line region of an active galactic nucleus (AGN), as the lack of a broad component in the forbidden lines rejects an outflow origin. This hypothesis is supported by the presence of high-ionization lines, as well as a spatial point-source component embedded within a smoother surface brightness profile. The mass of the black hole is log($M_{BH}/M_{\odot})=6.95{\pm}0.37$, and we estimate that it is accreting at 1.2 ($\pm$0.5) x the Eddington limit. The 1-8 $μ$m photometric spectral energy distribution (SED) from NIRCam and MIRI shows a continuum dominated by starlight and constrains the host galaxy to be massive (log M/M$_{\odot}$~9.5) and highly star-forming (SFR~30 M$_{\odot}$ yr$^{-1}$). Ratios of the strong emission lines show that the gas in this galaxy is metal-poor (Z/Z$_{\odot}$~0.1), dense (n$_{e}$~10$^{3}$ cm$^{-3}$), and highly ionized (log U~-2.1), consistent with the general galaxy population observed with JWST at high redshifts. We use this presently highest-redshift AGN discovery to place constraints on black hole seeding models and find that a combination of either super-Eddington accretion from stellar seeds or Eddington accretion from massive black hole seeds is required to form this object by the observed epoch.

Figures (14)

• Figure 1: 2D and 1D spectra of CEERS_1019 from three JWST/NIRSpec M gratings: G140M (top), G235M (middle), and G395M (bottom). The horizontal red dashed line identifies the central location of the source in the 2D spectrum and is the extraction center for our 1D spectra. Measured emission lines are indicated with purple dotted lines and discussed in Section 4. A description of the CEERS NIRSpec observations for this source is given in Section 2.1, and the data reduction process is described in Section 2.1.1.
• Figure 2: Comparison of the JWST/NIRSpec combined M grating spectrum when using the native pipeline pathloss correction (black) vs. without this step of the pipeline, but rather scaling the spectra to the measured JWST/NIRCam photometry (blue), as described in Fujimoto et al. (2023) and in Section 2.1.1. Our scaled spectrum (purple) highlights how the default pipeline pathloss correction underpredicts the total slit-loss correction for this source and that corrections to the NIRSpec spectrum are required for the flux calibration of resolved sources.
• Figure 3: The spectrum of CEERS_1019 obtained with JWST/NIRCam's wide-field slitless spectroscopy mode. This consists of spectra with both the column ("C"; blue) and row ("R"; purple) grisms, both taken with the F356W blocking filter, with a combined spectrum shown in black. While these data have a higher noise level than the NIRSpec spectra, we observe detections of the same$[\mathrm{O} \text{ II }]_{3727+3729}$, $[\mathrm{Ne} \text{ III }]_{3870}$, and bluer Balmer lines that we see in NIRSpec (Figure 5). While we do not use the grism measurements in this paper, these data highlight the utility of this mode for obtaining slitless measurements of modestly faint emission lines out to high redshifts.
• Figure 4: Combined JWST/NIRSpec spectrum from G140M + G235M + G395M of CEERS_1019, plotted in$\mathrm{F}_{\lambda}\left[10^{-19} \mathrm{erg} \mathrm{s}^{-1} \mathrm{~cm}^{-2} \mathring{\mathrm{A}}^{-1}\right]$ vs. observed wavelength $[\mu \mathrm{m}]$. Plotted in green is the fit to the continuum in the spectrum (see Section 3.1) plus the detected emission lines, as discussed in Section 4. We require an S/N $>2.3$ (with our simulation-estimated noise as described in Section 3.2) for a line to be considered detected.
• Figure 5: Fits to the emission lines identified in the JWST/NIRSpec spectrum of CEERS_1019. Each panel shows an individual emission-line fit, with the type of line profile as described in Section 3. The panels are plotted in$F_{\lambda}\left(10^{-19} \mathrm{erg} \mathrm{s}^{-1} \mathrm{~cm}^{-2} \mathring{\mathrm{A}}^{-1}\right)$ vs. observed wavelength ( $\mu \mathrm{m}$ ), are presented in order of increasing wavelength, and are scaled vertically to show the extent of the highlighted emission line. Emission-line values are tabulated in Table 3 and discussions of specific lines are given in Section 4.