Is GN-z11 powered by a super-Eddington massive black hole?

Abstract

Context. Observations of z ∼ 6 quasars powered by supermassive black holes (SMBHs; M<SUB>BH</SUB> ∼ 10<SUP>8 − 10</SUP> M<SUB>⊙</SUB>) challenge our current understanding of early black hole (BH) formation and evolution. The advent of the James Webb Space Telescope (JWST) has enabled the study of massive BHs (MBHs; M<SUB>BH</SUB> ∼ 10<SUP>6 − 7</SUP> M<SUB>⊙</SUB>) up to z ∼ 11, thus bridging the properties of z ∼ 6 quasars to their ancestors. <BR /> Aims: The JWST spectroscopic observations of GN-z11, a well-known z = 10.6 star-forming galaxy, have been interpreted with the presence of a super-Eddington (Eddington ratio ≡ λ<SUB>Edd</SUB> ∼ 5.5) accreting MBH. To test this hypothesis, we used a zoom-in cosmological simulation of galaxy formation and BH co-evolution. <BR /> Methods: We first tested the simulation results against the observed probability distribution function (PDF) of λ<SUB>Edd</SUB> found in z ∼ 6 quasars. Then, in the simulation we selected the BHs that satisfy the following criteria: (a) 10 < z < 11, (b) M<SUB>BH</SUB> > 10<SUP>6</SUP> M<SUB>⊙</SUB>. Next, we applied the extreme value statistics to the PDF of λ<SUB>Edd</SUB> resulting from the simulation. <BR /> Results: We find that the probability of observing a z ∼ 10 − 11 MBH accreting with λ<SUB>Edd</SUB> ∼ 5.5 in the volume surveyed by JWST is very low (< 0.2%). We compared our predictions with those in the literature, and discussed the main limitations of our work. <BR /> Conclusions: Our simulation cannot explain the JWST observations of GN-z11. This might be due to: (i) poor resolution and statistics in simulations, (ii) simplistic sub-grid models (e.g. BH accretion and seeding), (iii) uncertainties in the data analysis and interpretation.