On the rapid growth of SMBHs in high-z galaxies: the aftermath of Population III.1 stars

Mahsa Sanati, Julien Devriendt, SergioMartin-Alvarez, Adrianne Slyz, Jonathan C. Tan

First listed 2025-07-02 | Last updated 2025-07-02

Abstract

The vast amount of energy released by active galactic nuclei (AGN) is increasingly recognized as a key driver of evolution not only in massive galaxies and clusters, but also in low-mass dwarf galaxies. Despite this, their role in the early stages of galaxy formation and in self-regulating the rapid growth of the first and abundant supermassive black holes (SMBHs) remains poorly understood. Through new high-resolution zoom-in cosmological simulations, we follow the co-evolution of $10^5 M_\odot$ black hole seeds with their host galaxy. The simulated suite progressively spans physics ranging from no AGN feedback and Eddington-limited thermal feedback, to more complex setups including non-Eddington-limited thermal, kinetic and radiative feedback. Across all our models, we find that black hole seeds efficiently reach masses of $\sim10^7 M_\odot$ by z=8. Although they exhibit notably different mass growth histories, these latter seem unimpeded by the presence of AGN feedback. The simulation including radiative feedback is the most distinct, with super-Eddington episodes driving fast and mass-loaded gas outflows (exceeding 2500 km $s^{-1}$) up to $\sim$50 kpc, along with minor stellar mass suppression in the host galaxy. Our measurements are in broad agreement with moderate luminosity quasars recently observed by JWST, producing overmassive black holes, dynamical masses of $\sim10^{9.5} M_\odot$, and high, though short-lived, Eddington fraction accretion rates. These results advocate for a scenario where AGN feedback allows for rapid SMBH growth during the reionisation era, while driving winds that extend deep into the intergalactic medium - shaping host galaxies as well as more distant surroundings.

Short digest

High-resolution zoom-in simulations with Pop III.1 progenitor preheating follow 10^5 Msun seeds through a suite of AGN feedback modes (Eddington-limited thermal; non-Eddington thermal, kinetic, and radiative). Across all models the seeds grow efficiently to ~10^7 Msun by z≈8, with growth largely unimpeded by feedback; the radiative case shows brief super-Eddington bursts that launch fast, mass-loaded outflows (>2500 km s^-1) to ~50 kpc and slightly suppress stellar mass. The simulated systems resemble JWST moderate-luminosity quasars, yielding overmassive BHs, dynamical masses ~10^9.5 Msun, and short-lived high Eddington fractions. This argues that early AGN feedback coexists with rapid SMBH build-up while exporting energy and metals deep into the CGM/IGM.

Key figures to inspect

• Figure 1: Follow the multi-panel timelines to see how each feedback prescription changes BH mass growth, f_Edd spikes, gas inflow→outflow transitions, and the modest reduction in stellar mass; note the strong outflow signature in the ThermKinRad run coincident with super-Eddington peaks.
• Figure 2: Compare the PDFs of f_Edd across models to verify that most growth is near/below Eddington with only a small super-Edd tail, and assess how adding radiation shifts the high-f_Edd incidence.
• Figure 3: Examine the tracks in f_Edd–MBH space against the JDEEP points and the Eddington-limited reference to distinguish early burst-dominated growth (weak thermal-only) from self-regulated, gradual buildup (kinetic/radiative).
• Figure 4: Inspect the BH’s displacement from the galaxy center to gauge how orbital wandering modulates encounters with dense central gas and correlates with the most efficient accretion phases in each model.