Episodic super-Eddington accretion as a clue to Overmassive Black Holes in the early Universe
Abstract Early JWST observations are providing growing evidence for a ubiquitous population of accreting supermassive black holes (BHs) at high redshift, many of which appear overmassive compared to the empirically-derived local scaling relation between black hole mass and host galaxy stellar mass. In this study, we leverage predictions from the semi-analytical Cosmic Archaeology Tool (CAT) to reconstruct the evolutionary pathways for this overmassive BH population, investigating how they assemble over cosmic time and interact with their host galaxies. We find that the large $\\rm M_{BH}-M_{star}$ ratios can be explained if light and heavy BH seeds grow by short, repeated episodes of super-Eddington accretion, triggered by major galaxy mergers. On average, we find that BH-galaxy co-evolution starts in earnest only at z < 8, when ≃ 30% of the final galaxy stellar mass has formed outside the massive black hole host. Our model suggests that super-Eddington bursts of accretion last between 0.5 − 3 Myr, resulting in a duty cycle of 1 − 4% for the target BH sample. The boost in luminosity of BHs undergoing super-Eddington accretion helps to explain the luminosity function of Active Galactic Nuclei observed by JWST. At the same time, a large population of these overmassive BHs is predicted to be inactive, with Eddington ratios λEdd < 0.05, in agreement with recent observations.
Authors
- Raffaella Schneider (ORCID: https://orcid.org/0000-0001-9317-2888)
- Luca Graziani (ORCID: https://orcid.org/0000-0002-9231-1505)
- Alessandro Lupi (ORCID: https://orcid.org/0000-0001-6106-7821)
- Priyamvada Natarajan (ORCID: https://orcid.org/0000-0002-5554-8896)
- R. Maiolino (ORCID: https://orcid.org/0000-0002-4985-3819)
- Tommaso Zana (ORCID: https://orcid.org/0000-0003-4244-8527)
- Ignas Juodžbalis (ORCID: https://orcid.org/0009-0003-7423-8660)
- Alessandro Trinca (ORCID: https://orcid.org/0000-0002-1899-4360)
- Rosa Valiante (ORCID: https://orcid.org/0000-0003-3050-1765)
- Marta Volonteri (ORCID: https://orcid.org/0000-0002-3216-1322)
Institutions
- University of Insubria (IT)
- Centre National de la Recherche Scientifique (FR)
- University of Cambridge (GB)
- Astronomical Observatory of Rome (IT)
- Institut d'Astrophysique de Paris (FR)
- Yale University (US)
- Sorbonne Université (FR)
- Royal Observatory (GB)
- Istituto Nazionale di Fisica Nucleare, Sezione di Milano Bicocca (IT)
- Istituto Nazionale di Fisica Nucleare, Sezione di Roma I (IT)
- Sapienza University of Rome (IT)
- University of Edinburgh (GB)
Publication Details
- Journal
- Monthly Notices of the Royal Astronomical Society
- Published
- 2026-08-27
- DOI
- https://doi.org/10.1093/mnras/stag1608
- Citations
- 7
- Primary Topic
- Relativity and Gravitational Theory
- Type
- article
- Field-Weighted Citation Impact
- 9.08
Funders
- National Science Foundation
- John Templeton Foundation
- Gordon and Betty Moore Foundation
- Harvard University
- UK Research and Innovation
- European Commission
- Ministero dell’Istruzione, dell’Università e della Ricerca
- Science and Technology Facilities Council
- Kavli Institute for Theoretical Physics, University of California, Santa Barbara
- Amaldi Research Center