A high black-hole-to-host mass ratio in a lensed AGN in the early Universe

Early JWST observations have uncovered a population of red sources that might represent a previously overlooked phase of supermassive black hole growth1–3. One of the most intriguing examples is an extremely red, point-like object that was found to be triply imaged by the strong lensing cluster Abell 2744 (ref. 4). Here we present deep JWST/NIRSpec observations of this object, Abell2744-QSO1. The spectroscopy confirms that the three images are of the same object, and that it is a highly reddened (AV≃ 3) broad emission line active galactic nucleus at a redshift of zspec= 7.0451 ± 0.0005. From the width of Hβ (full width at half-maximum = 2,800 ± 250 km s−1), we derive a black hole mass of MBH=4−1+2×107M⊙. We infer a very high ratio of black-hole-to-galaxy mass of at least 3%, an order of magnitude more than that seen in local galaxies5and possibly as high as 100%. The lack of strong metal lines in the spectrum together with the high bolometric luminosity (Lbol= (1.1 ± 0.3) × 1045erg s−1) indicate that we are seeing the black hole in a phase of rapid growth, accreting at 30% of the Eddington limit. The rapid growth and high black-hole-to-galaxy mass ratio of Abell2744-QSO1 suggest that it may represent the missing link between black hole seeds6and one of the first luminous quasars7.