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

Abstract

Early JWST observations have uncovered a population of red sources that might represent a previously overlooked phase of supermassive black hole growth^1-3. 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 (A_V ≃ 3) broad emission line active galactic nucleus at a redshift of z_spec = 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 <math xmlns="http://www.w3.org/1998/Math/MathML"> <mrow> <msub><mrow><mi>M</mi></mrow> <mrow><mi>BH</mi></mrow> </msub> <mo>=</mo> <msubsup><mrow><mn>4</mn></mrow> <mrow><mo>-</mo> <mn>1</mn></mrow> <mrow><mo>+</mo> <mn>2</mn></mrow> </msubsup> <mo>×</mo> <mn>1</mn> <msup><mrow><mn>0</mn></mrow> <mrow><mn>7</mn></mrow> </msup> <mspace></mspace> <msub><mrow><mi>M</mi></mrow> <mrow><mo>⊙</mo></mrow> </msub> </mrow> </math> . 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 galaxies⁵ and possibly as high as 100%. The lack of strong metal lines in the spectrum together with the high bolometric luminosity (L_bol = (1.1 ± 0.3) × 10⁴⁵ erg 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 seeds⁶ and one of the first luminous quasars⁷.