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

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\(\alpha\)-break by Hubble and with a Ly\(\alpha\) 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\(\alpha\) redshift. We detect a significant broad (FWHM~1200 km/s) component in the H\(\beta\) 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 \(\mu\)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.