A CEERS Discovery of an Accreting Supermassive Black Hole 570 Myr after the Big Bang: Identifying a Progenitor of Massive z > 6 Quasars (2303.08918v2)

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.

• The paper reveals an early accreting SMBH at z ~8.7 using multi-instrument JWST CEERS data and MCMC spectral analysis.
• The paper employs imaging and spectroscopy to detect a broad Hβ line with a FWHM of ~1200 km/s, confirming active accretion.
• The paper highlights rapid SMBH growth in a star-forming, metal-poor galaxy, challenging conventional models of seed formation.

Analyzing the Discovery of an Early Accreting Supermassive Black Hole by Larson et al.

The paper entitled "A CEERS Discovery of an Accreting Supermassive Black Hole 570Myr after the Big Bang: Identifying a Progenitor of Massive z>6 Quasars" by Larson et al., published in The Astrophysical Journal Letters, presents the discovery of a supermassive black hole (SMBH) at a redshift of 8.679. Utilizing data from the Cosmic Evolution Early Release Science (CEERS) survey, including observations from JWST instruments, the authors provide a detailed analysis of a galaxy designated CEERS_1019.

Overview and Methodology

This paper makes use of data from various JWST instruments, specifically NIRSpec, MIRI, NIRCam, and the NIRCam/WFSS, to identify emission lines that indicate the presence of an active galactic nucleus (AGN). A Lyα-break galaxy previously detected by Hubble and analyzed using Keck’s spectroscopy provided the initial clue to the galaxy's significance, confirmed by the JWST data. The continuum emission and detected emission lines, including a prominent broad Hβ line with a full width at half maximum (FWHM) of approximately 1200 km s⁻¹, imply a massive black hole actively accreting material at a significant rate.

The authors employ an automated line-finding approach, which incorporates Monte Carlo Markov Chain (MCMC) methods for identifying and fitting emission features. Notably, they simulate line-injection tests to constrain uncertainties accurately, yielding robust measures of flux and velocity dispersion. The paper identifies the broad Hβ component, supporting the hypothesis of an AGN, and measures weak high-ionization and emission lines, further validating this conclusion.

Implications of the Research

The discovery of CEERS_1019 and its accreting SMBH provides insight into the early Universe's black hole formation and growth mechanisms. The mass of the black hole, approximately log(M_BH/M_⊙) = 6.95 ± 0.37, suggests rapid growth—a possibility given hypothesized super-Eddington accretion scenarios on smaller stellar-mass seeds. Conversely, the data do not rule out more massive seed scenarios such as direct collapse black holes (DCBHs).

Moreover, the broadband imaging and spectral energy distribution (SED) analysis infer a relatively metal-poor host galaxy, with an abundance of star formation activity (SFR ~ 30 M_⊙ yr⁻¹). The galactic structure, identified using NIRCam imaging, suggests morphological features consistent with early galactic mergers or significant star-forming regions, which might contribute to the black hole's accelerated growth.

Speculative Future Directions

The identification of such a high-redshift AGN challenges existing models of SMBH seed formation and early growth. This discovery points toward the need for further theoretical and observational pursuits to refine our understanding of early SMBHs. Future investigations should focus on uncovering additional high-redshift, lower mass black holes to address existing inconsistencies in seed formation theories. Such efforts may also refine estimates of how SMBHs contribute to the reionization epoch.

Lastly, the detection of CEERS_1019 within an overdense region implies other processes, possibly involving both AGN activity and star-forming galaxies, might affect ionization during cosmic reionization. JWST's extended capabilities will be indispensable in exploring these environments, uncovering the mysteries of early universe cosmology, and resolving questions surrounding black hole formation and evolution in the context of cosmic history.

Thus, this paper by Larson et al. not only provides evidence of rapid SMBH growth shortly after the Big Bang but also underscores the transformative role that advanced observational tools like JWST will play in unraveling the complexities of the high-redshift universe.