Theoretical Modelling of Early Massive Black Holes

TL;DR

The chapter surveys theoretical frameworks for the formation, growth, and observables of massive black holes in the first billion years, with a focus on interpreting JWST discoveries of abundant high-redshift AGN and LRDs. It catalogs seed formation channels (Pop III remnants, direct collapse via supermassive stars/quasi-stars, stellar-cluster runaway mergers, primordial BHs) and growth pathways (gas accretion, MBH mergers, stellar accretion), and surveys modeling approaches from analytical to cosmological simulations. It explains how MBH observables—AGN spectral energy distributions, obscuration, radio output, gravitational waves, and TDEs—are modeled and linked to underlying physics, including the roles of Eddington- and super-Eddington accretion and feedback processes. The discussion highlights JWST-era challenges to pre-JWST demographics, the potential need for exotic channels or rapid growth mechanisms, and the prospects for multi-messenger constraints (e.g., LISA) to illuminate MBH populations across cosmic time.

Abstract

These notes review theoretical models of massive black hole formation, growth and observables. They start with a brief summary of basic properties of massive black hole properties. The current view on massive black holes and active galactic nuclei at high redshift is then summarized, highlighting the JWST ``revolution'' and the questions raised by the recent observations. The notes then touch on massive black hole formation and growth mechanisms, emphasizing the processes at play at early cosmic times. Then techniques for modeling the cosmic massive black hole evolution, are reviewed with an emphasis on cosmological simulations, before approaching how observables are derived from models. They conclude with a section reflecting on the main questions on the JWST-discovered population in light of the material presented in the earlier sections.

Figures (13)

• Figure 1: Sketch of the physical scales characterizing galaxies and MBHs.
• Figure 2: AGN luminosity functions derived from JWST data mattheeLittleRedDots20242024ApJ...974..147LgreeneUNCOVERSpectroscopyConfirms2024, compared to pre-JWST expectations 2020MNRAS.495.3252S. Standard relations based on local sources have here been used to estimate the bolometric luminosities of high-z AGN.
• Figure 3: Relation between $M_{\rm BH}$ and host galaxy $M_{\rm star}$ for $z=0$ sources greeneIntermediateMassBlackHoles, high-z AGN using $M_{\rm BH}$ from the discovery papers (gray dots) and including modifications to account for broad line region size in super-Eddington sources 2024AA...689A.128L. The green contours show the region where a MBH population which intrinsically sits on the $z=0$ relation from greeneIntermediateMassBlackHoles is shifted when applying selection effects liTipIcebergOvermassive2024.
• Figure 4: Estimated MBH masses vs redshift for $z>6$ quasars 2023ARAA..61..373F and JWST-discovered MBHs at $z=4-11$harikaneJWSTNirspecFirst2023maiolinoJADESDiversePopulation2023greeneUNCOVERSpectroscopyConfirms20242024NatAs...8..126B2024ApJ...965L..21K, compared to growth tracks assuming different initial MBH masses and accretion rates.
• Figure 5: Sketch of how different patways to MBH formation can be viewed as a continuum, in dependence of the environmental conditions: strength and SED of the LW radiation, metallicity, cluster properties.