A small and vigorous black hole in the early Universe

Abstract

Several theories have been proposed to describe the formation of black hole seeds in the early Universe and to explain the emergence of very massive black holes observed in the first thousand million years after the Big Bang^1-3. Models consider different seeding and accretion scenarios^4-7, which require the detection and characterization of black holes in the first few hundred million years after the Big Bang to be validated. Here we present an extensive analysis of the JWST-NIRSpec spectrum of GN-z11, an exceptionally luminous galaxy at z = 10.6, revealing the detection of the [NeIV]λ2423 and CII*λ1335 transitions (typical of active galactic nuclei), as well as semi-forbidden nebular lines tracing gas densities higher than 10⁹ cm^-3, typical of the broad line region of active galactic nuclei. These spectral features indicate that GN-z11 hosts an accreting black hole. The spectrum also reveals a deep and blueshifted CIVλ1549 absorption trough, tracing an outflow with velocity 800-1,000 km s^-1, probably driven by the active galactic nucleus. Assuming local virial relations, we derive a black hole mass of $\log \left(M_{\mathrm{BH}}/M_{\odot }\right)=6.2\pm 0.3$ , accreting at about five times the Eddington rate. These properties are consistent with both heavy seeds scenarios and scenarios considering intermediate and light seeds experiencing episodic super-Eddington phases. Our finding explains the high luminosity of GN-z11 and can also provide an explanation for its exceptionally high nitrogen abundance.

Fig. 1. Magnification of the spectra of GN-z11 around specific spectral features of interest, along with their single and multiple Gaussian models (Methods).

Dashed lines indicate the rest-frame wavelengths of the lines at z = 10.603. a, [Neiv]λλ2422,2424 doublet; b, NIII] multiplet, illustrating the detection of the resolved Niii]λ1754 emission; c, NIV] doublet, showing the absence of [Niv]λ1483 despite the strong Niv]λ1486; d, CIV blueshifted absorption trough and redshifted resonant emission, compared with the CIV P-Cygni profile observed in low-metallicity, young star-forming galaxies (stack: orange dashed line; most extreme case: orange dotted line), showing inconsistency with the latter. e, CII/CII*λλ1334,1335 doublet (seen in emission, without P-Cygni, only in type 1 AGN); f, Expected flux of the NIV1718 line in the case that NIV]1486 was associated with WR stars. In a–c, e and f, the continuum is subtracted, whereas in d the continuum is normalized to one. The grey dotted lines indicate the noise level (1σ).

Fig. 2. Flux ratios of density-sensitive nitrogen lines as a function of hydrogen gas density, n_H.

A large range of Cloudy models (Methods) are compared with the values observed in GN-z11. Models with metal-poor (Z_neb = 0.1Z_⊙) and metal-rich (Z_neb = 1Z_⊙) gas are shown with solid lines and dashed lines, respectively (colour-coded according to the ionization parameter U), in the scenario in which either an AGN (filled symbols demarcating different black body temperatures for the accretion disc, T_AGN) or stellar populations (open markers for various ages, t_*) is responsible for the incident radiation field. a, [Niv]λ1483/Niv]λ1486 flux ratio. b, Ratio of Niii]λ1754 to total flux of the multiplet. The black dashed lines and blue-shaded regions (in decreasing darkness for 1σ, 2σ and 3σ confidence level as indicated) show the observed fractional contribution of Niii]λ1754 and upper limit on [Niv]λ1483/Niv]λ1486 obtained for GN-z11, indicating that the gas emitting these lines has high density (n_H ≳ 10⁹ cm⁻³ at 3σ). The light-green-shaded areas highlight the range of densities typical of the broad line regions (BLRs), whereas the grey-shaded regions highlight the range of densities typical of the ionized interstellar medium (ISM).

Fig. 3. Black hole mass as a function of redshift (on a logarithmic scale) and age of the Universe.

The black hole mass inferred for GN-z11 is shown with the large golden symbol. The red-shaded region indicates the evolution expected in the case of super-Eddington accretion at the level inferred for GN-z11. The darker-blue-shaded region shows the black hole mass evolution assuming Eddington-limited accretion, whereas the lighter-blue-shaded region shows the case of evolution in the case of sub-Eddington accretion (between 0.1 and 1 the Eddington rate). The horizontal grey-shaded regions indicate the range of black hole seeds expected by different scenarios. Solid and dashed lines indicate the evolutionary tracks of various simulations and models^,, that can reproduce the GN-z11 black hole mass, with different seeding and accretion rate assumptions, as detailed in the Methods. The small grey symbols indicate the black holes measured in quasars (QSOs) at z ≈ 6–7.5 (refs. ^,) (whose representative 1σ error bar is shown in the top left), most of which can originate from a progenitor such as the black hole in GN-z11.

Fig. 4. Black hole versus stellar mass diagram.

The location of GN-z11 (large golden symbol) is compared with local galaxies as indicated by the small red symbols and their best-fit relation (black solid line and uncertainty traced by the grey-shaded region). The grey symbols show the values estimated for quasars (QSOs) at z ≈ 6−7 (ref. ), although in these cases the galaxy mass is inferred from dynamical tracers. The blue symbols are AGN at z > 4 for which the black hole and galaxy stellar mass has been measured with JWST data (Methods) using the same calibration as in ref.  for consistency.

Extended Data Fig. 1. Zoom in on the additional emission lines fitted.

a) MgIIλ2796,2804 doublet; b) HeIIλ1640; c) Lyα, NVλ1238,1242 doublet (undetected) and SiIIλ1260,1264 (undetected), corrected for the Lyα damping wing; d) Ciii]λ1906,1908 doublet. As the doublet is unresolved, the fit turns out degenerate between line width and fluxes of the two components; moreover it is also contributed to by star formation in the host galaxy (see text for details); e) [Neiii]λ3869 profile compared with the Balmer lines Hδ and Hγ. In all panels, the continuum is subtracted. The black dotted lines indicate the 1sigma noise level.

Extended Data Fig. 2. NV/CIV versus NV/HeII flux ratio diagram.

GN-z11 (golden circle) is compared with the ratios observed for the broad lines of type 1 AGN (purple stars), and for the NLR of type 2 AGN (red squares), illustrating that the non-detection of NV for GN-z11 is not constraining and consistent with the AGN scenario.

Extended Data Fig. 3. CIII]/CIV versus CIII]/HeII flux ratio diagrams.

GN-z11 (golden circle) is compared with: a) the AGN-NLR models (red squares) by and SF galaxies (blue stars) by (left) and with b) the AGN-NLR models (red squares) and SF models (blue triangles) by (centre). All models have been chosen in a low metallicity range, around the value inferred by for GN-z11. c) Comparison of GN-z11 with the ratios observed for the broad lines of type 1 AGN (purple circles), narrow lines of type 2 AGN (red squares), and starburst galaxies (blue stars).

Extended Data Fig. 4. Flux ratios of density-sensitive nitrogen lines as a function of hydrogen gas density, n_H.

Same as Fig. 2 but where we have separated the photoionization models for AGN (left) and Star Forming galaxies (right).

Extended Data Fig. 5. Low resolution (prism) spectrum of GN-z11.

Left: Observed prism spectrum (black solid) compared with the (maximum) contribution from the host galaxy of the AGN as inferred by (orange dotted), and the nebular emission inferred from a simple Cloudy model (purple dashed) normalized to the Hγ flux not included in the galaxy model. Right: Spectrum subtracted of the galactic and nebular continua, in a log-log scale, whose regions not affected by emission lines (solid black) have been fitted with a simple powerlaw (red-dashed) resulting into a slope of −2.26 ± 0.10, consistent with the slope expected for an accretion disc (−2.33, dotted green line).