Too many or too massive? Investigating the high-$z$ demography of active SMBHs from JWST
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| Main Authors: | , , , , , , , , , , , , , , |
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| Format: | Preprint |
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2026
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| author | Roberts, Daniel Shankar, Francesco Cammelli, Vieri Fontanot, Fabio Trinca, Alessandro Bisigello, Laura Bonta, Elena Dalla Fu, Hao Gilli, Roberto Grazian, Andrea Graziani, Luca Lapi, Andrea Menci, Nicola Scholtz, Jan Varadarajan, Karthik Mahesh |
| author_facet | Roberts, Daniel Shankar, Francesco Cammelli, Vieri Fontanot, Fabio Trinca, Alessandro Bisigello, Laura Bonta, Elena Dalla Fu, Hao Gilli, Roberto Grazian, Andrea Graziani, Luca Lapi, Andrea Menci, Nicola Scholtz, Jan Varadarajan, Karthik Mahesh |
| contents | Recent JWST observations have unveiled a numerous population of low-luminosity active galactic nuclei (AGN) at $4< z<10$, with space densities roughly an order of magnitude above pre-JWST estimates, and many of these AGN have masses orders of magnitude above the local black hole mass-stellar mass ($M_{\rm BH}-M_{*}$) scaling relations. We investigate the consistency of these observations within a data-driven framework that links the galaxy stellar mass function to the supermassive black hole (SMBH) mass function and AGN luminosity functions using different $M_{\rm BH}-M_{*}$ relations and the observed Eddington-ratio distribution. By comparing our predictions against observed AGN luminosity functions at $z\sim 5.5$ we find that observations can be reproduced either by highly-elevated $M_{\rm BH}-M_{*}$ relations paired with low duty cycles, or moderate relations with higher duty cycles. Through the Soltan argument, we find that $M_{\rm BH}-M_{*}$ relations that are modestly above the local relation for AGN produce consistency between multiple tracers of the SMBH demography at $z\sim 5.5$, while more extreme normalisations would require a weakly-evolving luminosity function at $z> 5.5$. Continuity-equation modelling shows that initially high $M_{\rm BH}-M_{*}$ relations predict a strong two-phase evolutionary scenario and very steep low-mass SMBH mass functions in tension with several current estimates, while more moderate relations generate local SMBH mass functions in better agreement with present determinations and near-constant scaling relations. Our results favour a scenario where SMBHs at $z \sim 5$ on average lie modestly above local AGN scaling relations, with elevated but physically plausible duty cycles. Future wide-field clustering and demographic studies will help break the remaining degeneracies between SMBH scaling relations and AGN duty cycles at early cosmic times. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2601_23250 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Too many or too massive? Investigating the high-$z$ demography of active SMBHs from JWST Roberts, Daniel Shankar, Francesco Cammelli, Vieri Fontanot, Fabio Trinca, Alessandro Bisigello, Laura Bonta, Elena Dalla Fu, Hao Gilli, Roberto Grazian, Andrea Graziani, Luca Lapi, Andrea Menci, Nicola Scholtz, Jan Varadarajan, Karthik Mahesh Astrophysics of Galaxies Recent JWST observations have unveiled a numerous population of low-luminosity active galactic nuclei (AGN) at $4< z<10$, with space densities roughly an order of magnitude above pre-JWST estimates, and many of these AGN have masses orders of magnitude above the local black hole mass-stellar mass ($M_{\rm BH}-M_{*}$) scaling relations. We investigate the consistency of these observations within a data-driven framework that links the galaxy stellar mass function to the supermassive black hole (SMBH) mass function and AGN luminosity functions using different $M_{\rm BH}-M_{*}$ relations and the observed Eddington-ratio distribution. By comparing our predictions against observed AGN luminosity functions at $z\sim 5.5$ we find that observations can be reproduced either by highly-elevated $M_{\rm BH}-M_{*}$ relations paired with low duty cycles, or moderate relations with higher duty cycles. Through the Soltan argument, we find that $M_{\rm BH}-M_{*}$ relations that are modestly above the local relation for AGN produce consistency between multiple tracers of the SMBH demography at $z\sim 5.5$, while more extreme normalisations would require a weakly-evolving luminosity function at $z> 5.5$. Continuity-equation modelling shows that initially high $M_{\rm BH}-M_{*}$ relations predict a strong two-phase evolutionary scenario and very steep low-mass SMBH mass functions in tension with several current estimates, while more moderate relations generate local SMBH mass functions in better agreement with present determinations and near-constant scaling relations. Our results favour a scenario where SMBHs at $z \sim 5$ on average lie modestly above local AGN scaling relations, with elevated but physically plausible duty cycles. Future wide-field clustering and demographic studies will help break the remaining degeneracies between SMBH scaling relations and AGN duty cycles at early cosmic times. |
| title | Too many or too massive? Investigating the high-$z$ demography of active SMBHs from JWST |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2601.23250 |