A small and vigorous black hole in the early Universe (2305.12492v2)

Abstract: Multiple 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 billion years after Big Bang. Models consider different seeding and accretion scenarios, which require the detection and characterisation of black holes in the first few hundred million years after 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]2423 and CII*1335 transitions (typical of Active Galactic Nuclei, AGN), as well as semi-forbidden nebular lines tracing gas densities higher than 10^9 cm-3, typical of the Broad Line Region of AGN. These spectral features indicate that GN-z11 hosts an accreting black hole. The spectrum also reveals a deep and blueshifted CIV1549 absorption trough, tracing an outflow with velocity 800-1000 km/s, likely driven by the AGN. Assuming local virial relations, we derive a black hole mass of log(M_BH/Msun) = 6.2 +- 0.3, accreting at about 5 times the Eddington rate. These properties are consistent with both heavy seeds scenarios, or scenarios envisaging intermediate/light seeds experiencing episodic super-Eddington phases. Our finding naturally explains the high luminosity of GN-z11 and can also provide an explanation for its exceptionally high nitrogen abundance.

• The paper reveals a rapidly accreting black hole in GN-z11 at z=10.6 confirmed by distinct [NeIV] and CII* spectral lines.
• It quantifies the black hole mass at log(MBH/M⊙)=6.2 with accretion rates nearly five times the Eddington limit and detects blue-shifted CIV absorption indicating outflows of 800–1000 km/s.
• The study supports black hole seed formation models and underscores the role of AGN feedback in early galaxy evolution and rapid black hole growth.

Analysis of a Small and Vigorous Black Hole in the Early Universe

The paper examines a unique astrophysical phenomenon—a small but actively accreting black hole in the early Universe, using spectroscopic data obtained from the JWST-NIRSpec. This investigation focuses on the black hole residing in GN-z11, an exceptionally luminous galaxy situated at a redshift of z=10.6. The research provides a nuanced understanding of the characteristics of black hole seeds during the formative epochs of the Universe and links the observations with prevailing theories of black hole formation and growth.

Key Findings

The paper reveals the detection of the [NeIV]$\lambda$2423 and CII*$\lambda$1335 transitions in the spectral analysis of GN-z11, which are indicative of an Active Galactic Nucleus (AGN). These transitions, alongside semi-forbidden lines typical of high-density regions associated with AGN, point to the presence of a rapidly accreting black hole. The derived black hole mass is $\rm \log{(M_{BH}/M_{\odot})}=6.2\pm 0.3$, accreting at roughly five times the Eddington rate—a significant observation that supports scenarios of both heavy and intermediate/light seeds experiencing episodic super-Eddington accretion phases.

In addition to these findings, the spectrum exhibits a profound and blue-shifted CIV$\lambda$1549 absorption trough, hinting at outflows with velocities between 800-1000 km/s, likely driven by the AGN activity. This aspect distinguishes it from typical starburst galaxies, suggesting significant AGN influence.

Implications

The implications of this research are extensive, affecting our understanding of early Universe astrophysics and black hole evolution. The proposed black hole seed scenarios include heavy seed formation through direct collapse mechanisms and lighter seeds from Population III stars or star cluster mergers. The observation of an accreting black hole in GN-z11 with these specific characteristics provides a crucial empirical benchmark to validate these models within cosmological simulations. It adds depth to the discussion on how supermassive black holes might grow so rapidly in the early Universe and the conditions necessary for such growth.

Furthermore, understanding black holes' role in the initial stages of galaxy formation could provide insights into the earliest phases of galactic evolution and the interplay between black holes and their host galaxies. The presence of high-velocity outflows associated with AGN activity underscores the broad impact AGNs can have, potentially influencing star formation rates and mechanical feedback processes within the galaxy and the surrounding interstellar medium.

Outlook and Future Directions

Future developments in astronomical instruments and survey capabilities, including deeper and more refined follow-up observations, will likely enhance the precision of black hole mass estimations and accretion rate calculations. Such advances are anticipated to provide further insight into the frequency and distribution of accreting black holes at high redshifts, revealing more about their environmental conditions and formation mechanisms.

The paper's results also prompt additional inquiries into how prevalent such systems are in the early Universe and whether similar accretion scenarios are common among other high-redshift AGNs. The challenges remaining involve disentangling the contributions of various astrophysical processes in these densely packed systems while leveraging comparative studies with local Universe AGNs. Ongoing efforts in this domain may elucidate the broader cosmic evolution narrative and refine the understanding of black hole physics through the cosmic epochs.