What is the origin of the JWST SMBHs?

TL;DR

This work develops a fast semi-analytical framework that uses the extended Press-Schechter formalism to directly evolve SMBH and host-galaxy properties, avoiding computationally expensive halo merger trees. By solving coupled growth equations for BH and stellar masses with mergers, accretion, SN feedback, and AGN feedback, and by exploring seed masses $m_{ m seed}$ and seed-halo thresholds $M_{ m seed}$ under different merger efficiencies $p_{ m BH}$, the authors test light versus heavy SMBH seeding scenarios against JWST, pre-JWST, and PTA GW data. The results show JWST high-redshift SMBHs favor light seeds when $p_{ m BH} \sim 1$, while lower merger efficiency $p_{ m BH} \sim 0.1$ shifts preference toward heavier seeds; other SMBH datasets prefer heavier seeds across both merger regimes. The model delivers BH mass–stellar mass relations consistent with high-$z$, PTA GW, and local inactive galaxies data and outperforms simple power-law fits; including a lognormal scatter in predictions improves the fit without altering the qualitative seed-formation conclusions. The approach provides a rapid, scalable tool to constrain SMBH seeding and co-evolution, with potential connections to the stochastic GW background at higher frequencies.

Abstract

We present a new semi-analytical model for the evolution of galaxies and supermassive black holes (SMBHs) that is based on the extended Press-Schechter formalism and phenomenological modelling of star formation. The model yields BH mass-stellar mass relations that reproduce both the JWST and pre-JWST observations. If the efficiency for BH mergers is high the JWST data prefer light seeds while the pre-JWST data prefers heavy seeds. The fit improves for a smaller merger efficiency, $O(0.1)$, for which both data prefer heavy seeds, while also accommodating the PTA GW background data.

Figures (9)

• Figure 1: Comparisons of model predictions for the stellar mass-BH mass relation with high-$z$ observations on the left and with low-$z$ observations on the right. The solid lines show the evolution of light seeds ($m_{\rm seed}=100\,M_{\odot}$ with $M_{\rm seed}=3\times10^4\,M_{\odot}$), and dashed lines show the evolution of heavy seeds ($m_{\rm seed}=10^5\, M_{\odot}$ with $M_{\rm seed}=3\times 10^{7}\, M_{\odot}$), both for $p_{\rm BH}=1$.
• Figure 2: Fits to stellar mass-BH mass data as functions of the seed BH mass $m_{\rm seed}$ and minimal halo mass $M_{\rm seed}$, where the seeds are inserted at $z_{\rm seed} = 20$ with $p_{\rm BH}=1$ in solid and $p_{\rm BH}=0.1$ in dashed. Upper left: High-$z$ quasar data compiled in 2021ApJ...914...36I. Upper right: High-$z$ observations with JWST 2023AA...677A.145U2023ApJ...953L..29L2023ApJ...959...39HBogdan:2023ilu2023Natur.621...51DMaiolino:2023bpi2023arXiv230904614Y. Lower left: Low-z AGNs as compiled in 2015ApJ...813...82R. Lower right: Low-$z$ IGs 2015ApJ...813...82R.
• Figure 3: Comparisons of model predictions for the stellar mass-BH mass relation with high-$z$ observations on the left and with low-$z$ observations on the right. The solid lines show the best fit for $p_{\rm BH} = 0.1$ to the JWST data, and the dashed lines show the best fit to the rest of the SMBH data. The best-fit parameter values are given in Table \ref{['tab:comparison']}.
• Figure 4: Fits to stellar mass-BH mass data: the red posteriors show the fit to the JWST data and the gray posteriors show the fit combining the low-$z$ data and the high-$z$ quasar data.
• Figure S1: Calculations of the growth rates of DM halos. The solid curves are obtained using Eq. \ref{['eq:Mdot']} and used in our analysis. The dashed curves show for comparison the estimates derived in Correa:2014xma, which are based on finding the average mass of the main progenitor.