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Peer-reviewedCC BYMonthly Notices of the Royal Astronomical Society

Episodic super-Eddington accretion as a clue to overmassive black holes in the early Universe

  • Alessandro Trinca1,2,3,4
  • Rosa Valiante2
  • Raffaella Schneider5,2,3,6
  • Ignas Juodžbalis7
  • R. Maiolino8,7
  • Luca Graziani5,2,3
  • Alessandro Lupi1,9
  • Priyamvada Natarajan10,11,12
  • Marta Volonteri13
  • Tommaso Zana5,2,3
13 affiliations
  1. 1Como Lake Center for Astrophysics, DiSAT, Università degli Studi dell’Insubria , Via Valleggio 11, I-22100 Como ,
  2. 2INAF/Osservatorio Astronomico di Roma , Via Frascati 33, 00040 Monte Porzio Catone ,
  3. 3INFN, Sezione Roma1, Dipartimento di Fisica, ‘Sapienza’ Università di Roma , Piazzale Aldo Moro 2, I-00185 Roma ,
  4. 4Institute for Astronomy, University of Edinburgh, Royal Observatory , Blackford Hill, Edinburgh EH9 3HJ ,
  5. 5Dipartimento di Fisica, ‘Sapienza’ Università di Roma , Piazzale Aldo Moro 2, I-00185 Roma ,
  6. 6Sapienza School for Advanced Studies , Viale Regina Elena 291, I-00161 Roma ,
  7. 7Kavli Institute for Cosmology, University of Cambridge , Madingley Road, Cambridge CB3 0HA ,
  8. 8Cavendish Laboratory, University of Cambridge , 19 JJ Thomson Avenue, Cambridge CB3 0HE ,
  9. 9INFN, Sezione di Milano-Bicocca , Piazza della Scienza 3, I-20126 Milano ,
  10. 10Department of Astronomy, Yale University , New Haven, CT 06511 ,
  11. 11Department of Physics, Yale University , New Haven, CT 06511 ,
  12. 12Yale Center for Astronomy & Astrophysics, Yale University , New Haven, CT 06520 ,
  13. 13Institut d’Astrophysique de Paris, Sorbonne Université, CNRS , UMR 7095, 98 bis bd Arago, F-75014 Paris ,
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Abstract

Early James Webb Space Telescope (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 BH 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 it MBH − it Mstar 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 lt 8, when ≃ 30 per cent of the final galaxy stellar mass has formed outside the massive BH host. Our model suggests that super-Eddington bursts of accretion last between 0.5 and 3 Myr, resulting in a duty cycle of 1 − 4 per cent 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 λ Edd lt 0.05, in agreement with recent observations.

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Cite

BibTeXRIS
BibTeX
@article{trinca2026episodic,
  title = {{Episodic super-Eddington accretion as a clue to overmassive black holes in the early Universe}},
  author = {Alessandro Trinca and Rosa Valiante and Raffaella Schneider and Ignas Juodžbalis and R. Maiolino and Luca Graziani and Alessandro Lupi and Priyamvada Natarajan and Marta Volonteri and Tommaso Zana},
  journal = {Monthly Notices of the Royal Astronomical Society},
  year = {2026},
  month = aug,
  doi = {10.1093/mnras/stag1608},
  url = {https://doi.org/10.1093/mnras/stag1608},
  note = {CC BY},
}
RIS
TY  - JOUR
TI  - Episodic super-Eddington accretion as a clue to overmassive black holes in the early Universe
AU  - Alessandro Trinca
AU  - Rosa Valiante
AU  - Raffaella Schneider
AU  - Ignas Juodžbalis
AU  - R. Maiolino
AU  - Luca Graziani
AU  - Alessandro Lupi
AU  - Priyamvada Natarajan
AU  - Marta Volonteri
AU  - Tommaso Zana
PY  - 2026
DA  - 2026/08/27
JO  - Monthly Notices of the Royal Astronomical Society
DO  - 10.1093/mnras/stag1608
UR  - https://doi.org/10.1093/mnras/stag1608
AB  - Early James Webb Space Telescope (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 BH 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 it M_BH − it 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 lt 8, when ≃ 30 per cent of the final galaxy stellar mass has formed outside the massive BH host. Our model suggests that super-Eddington bursts of accretion last between 0.5 and 3 Myr, resulting in a duty cycle of 1 − 4 per cent 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 λ _Edd lt 0.05, in agreement with recent observations.
SN  - 0035-8711
SN  - 1365-2966
SN  - 1365-8711
ER  -