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

TL;DR

The study investigates how massive black holes form and grow in the early Universe and what ultimately halts their growth. Using three SEEDZ cosmological volumes with detailed BH accretion, feedback, and dynamical friction models, the authors find that short bursts of super-Eddington accretion can build MBHs up to ~$10^6$ solar masses by $z=12.5$, but the associated feedback unbinds gas from the host halo, effectively quenching further growth. The final MBH mass appears to be governed by the halo's binding energy rather than gas exhaustion, implying a ceiling at this epoch unless feedback is unusually weak or replenishment occurs via mergers or cosmic web accretion. These results have implications for interpreting JWST observations of high-redshift quasars and guide future modeling and observational tests of early black hole-galaxy coevolution.

Abstract

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$_\odot$.

Figures (12)

• Figure 1: The growth of the most massive black holes across each of the three SEEDZ volumes (Rarepeak,Normal1, Normal2). Each simulation has now reached $z = 12.5$, with the most massive MBH in each realization now above $10^6$$\rm{M_{\odot}}$. The majority of MBHs however lie within a factor of a few of their initial seed mass. We show the growth history of the top 5 most massive MBHs in each realisation as colored lines.
• Figure 2: Halo mass functions (HMFs) for the 3 simulation regions at $z=12.5$. We colour mass bins containing MBHs of mass greater than 10$^5$ and 10$^6$ M$_\odot$ in blue and red, respectively. Note that the heights of these coloured bins have not been altered from the original HMF, therefore the heights do not indicate number of halos containing MBHs.
• Figure 3: For the top 5 most massive MBHs by $z=12.5$ in each simulation, we show the MBH growth rate expressed as the ratio of the accretion rate to the Eddington rate, as a function of time since the formation of the MBH (blue). We also show the ratio of the mass of the MBH to the remaining gas mass within its host halo (red), as identified with the Subfind halo finder. We show the end point of the simulations as a black vertical line where appropriate.
• Figure 4: For the top 5 most massive MBHs by $z=12.5$ in each simulation, we show the combined mass in all stars and BHs within its host halo, as a function of time since the formation of the central MBH (purple). We also show the remaining gas mass within the halo (orange). Note that this data was taken from snapshots, with a lower output frequency than the black hole data shown in Figure \ref{['fig:edd1']}. We show the point where the MBH transitions from super- to sub-Eddington growth as a vertical dashed line, and show the end point of the simulations as a black vertical line where appropriate. As MBH accretion shuts off, the combined mass in stars and MBHs does not increase. Therefore, the formation of additional stars and/or MBHs is not responsible for cutting off the primary MBH's accretion supply.
• Figure 5: Projections of the halo containing N1BH2 before (left), during (center) and after (right) the accretion cut-off. The top 2 panels show density projections, while the bottom 2 panels show temperature projections. Scale lines are given in each panel to indicate the scale of each projection. BHs, PopIII stars and PopII stellar cluster particles are shown as black, blue and orange dots, respectively. We show the virial radius of the halo as a circle. We include values for the virial mass, virial radius, redshift and black hole mass.