Black Hole Feedback, Galaxy Quenching and Outflows at Cosmic Dawn: Analysis of the SEEDZ Simulations

Here we analyse the growth and feedback effects of massive black holes (MBHs) in the SEEDZ simulations. The most massive black holes grow to masses of $\sim10^{6}$ M$\odot$ by $z=12.5$ during short bursts of super-Eddington accretion, sustained over a period of 5-30 Myr. We find that the determining factor that cuts off this initial growth is feedback from the MBH itself, rather than nearby supernovae or exhausting the available gas reservoir. Our simulations show that for the most actively accreting MBHs, feedback completely evacuates the gas from the host halo and ejects it into the inter-galactic medium. Despite implementing a relatively weak feedback model, the energy injected into the gas surrounding the MBH exceeds the binding energy of the halo. These results either indicate that MBH feedback in the early ($Λ$CDM) Universe is much weaker than previously assumed, or that at least some of the high redshift galaxies we currently observe with JWST formed via a two-step process, whereby a MBH initially quenches its host galaxy and later reconstitutes its baryonic reservoir, either through mergers with gas rich galaxies or from accretion from the cosmic web. Moreover, the maximum black hole masses that emerge in SEEDZ are effectively set by a combination of MBH feedback modelling and the binding potential of the host halo. Unless feedback is extremely ineffective at early times (for example if growth is merger dominated rather than accretion dominated or feedback is contained close to the MBH) then the maximum mass of black holes at redshift before 12.5 should not significantly exceed $10^6$ M$\odot$.

💡 Research Summary

The paper presents a comprehensive analysis of massive black hole (MBH) growth and feedback in the SEEDZ suite of cosmological simulations, which are designed to confront the wealth of high‑redshift observations now available from JWST. Using the moving‑mesh code AREPO2, the authors simulate three distinct regions (Rarepeak, Normal1, Normal2) with fully coupled models for Population III/II star formation, supernova feedback, metal enrichment, and both light (∼10² M⊙) and heavy (∼10⁴ M⊙) black‑hole seed formation.
Black‑hole accretion is treated with a Bondi‑Hoyle‑Lyttleton prescription, but because the Bondi radius is not resolved for most seeds, a Gaussian kernel is employed to weight gas cells within an accretion sphere of radius 5 Δx_min. The kernel accounts for local gas density, sound speed, bulk velocity, and a vorticity term ω that suppresses accretion of high‑angular‑momentum gas. The final accretion rate combines a standard Bondi term with a vorticity‑adjusted term, ensuring that turbulent, low‑vorticity gas is preferentially captured.
Feedback is injected thermally into the same accretion region. The thermal coupling efficiency is fixed at f_c = 0.05, while the radiative efficiency ε depends on the accretion regime. For sub‑Eddington rates, ε is derived from the ISCO radius assuming a spin a = 0.7, yielding ε ≈ 0.1. In the super‑Eddington regime the authors adopt the slim‑disc model of Madau et al. (2014), which reduces ε dramatically and therefore weakens feedback at very high accretion rates. Energy injection per timestep is capped at five times the cell’s internal energy to maintain numerical stability.
Because the dark‑matter particle mass is relatively large, the authors add a dynamical‑friction correction based on the Chandrasekhar formula, with a Coulomb logarithm set by the softening length (∼20 × the minimum gas cell size). This correction is applied only to black holes whose mass exceeds five times the dark‑matter particle mass; stellar dynamical friction is neglected at the current resolution.
The simulations reveal that the most massive black holes in each volume experience short, intense bursts of super‑Eddington accretion lasting 5–30 Myr, during which they grow from their seed masses to ≳10⁶ M⊙ by redshift z ≈ 12.5. Crucially, the termination of this rapid growth is not caused by depletion of the host halo’s gas reservoir nor by supernova feedback, but by the black hole’s own feedback. The injected thermal energy exceeds the binding energy of the host halo, driving a near‑complete evacuation of gas from the halo and launching powerful outflows into the intergalactic medium.
The authors argue that, given the relatively weak feedback model (f_c = 0.05, purely thermal), the fact that feedback still dominates suggests that early‑Universe black‑hole feedback may be far more efficient than previously assumed, or that the observed high‑z galaxies with over‑massive black holes have undergone a two‑step evolutionary path: an initial quenching phase driven by the MBH, followed by a re‑accretion phase via gas‑rich mergers or cosmic‑web inflows that rebuilds the stellar component. This scenario naturally explains the elevated M_BH/M_* ratios (∼10⁻²) reported in JWST surveys, which differ from the local relation (∼10⁻⁴).
The paper also places an upper bound on early black‑hole masses: unless feedback is dramatically ineffective (e.g., growth dominated by mergers rather than accretion, or feedback confined to sub‑parsec scales), MBHs are unlikely to exceed ∼10⁶ M⊙ before z ≈ 12.5. This limit is set jointly by the feedback implementation and the depth of the host halo’s potential well.
Limitations are acknowledged. The Bondi radius is unresolved for most seeds, introducing uncertainty in the accretion rates. Only thermal feedback is modeled; kinetic modes such as jets or winds, which could alter the coupling efficiency, are omitted. The dynamical‑friction treatment neglects stellar contributions, and the relatively coarse dark‑matter particle mass necessitates a correction that may not capture all small‑scale dynamics.
In summary, the SEEDZ simulations demonstrate that early massive black holes can grow rapidly to ∼10⁶ M⊙, but their own feedback quickly self‑regulates further growth by evacuating the host halo’s gas. This self‑quenching sets a natural ceiling on black‑hole masses at very high redshift and provides a plausible framework for interpreting the over‑massive black holes observed by JWST, either by invoking stronger early feedback or a two‑stage galaxy evolution involving post‑quenching gas replenishment. Future work with higher resolution, multi‑mode feedback, and refined dynamical‑friction modeling will be essential to test these conclusions.