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Abstract The accretion and feedback processes governing supermassive black hole (SMBH) growth span an enormous range of spatial scales, from the Event Horizon to the circumgalactic medium. Recent general relativistic magnetohydrodynamic (GRMHD) simulations demonstrate that strong magnetic fields can substantially suppress gas accretion onto black holes. These simulations show that magnetic fields create magnetically arrested disk states, reducing inflow rates by up to 2 orders of magnitude relative to classical predictions. We incorporate this magnetic suppression prescription from recent GRMHD studies into DarkSage, a semianalytic model that tracks SMBH and galaxy coevolution over cosmic time. Implementing the suppression across different accretion rate regimes, we explore its impact on the distribution of black hole masses, stellar masses in galaxies, and active galactic nucleus (AGN) luminosities. We find that restricting suppression to sub-Eddington accretors (f_Edd < 3 × 10⁻³) and rescaling AGN feedback efficiencies gives simultaneous agreement with the observed local distributions of both galaxy and black hole masses. At early cosmic times (z >  6), super-Eddington growth episodes dominate in our model, reproducing the high number densities of luminous AGN recently discovered by the James Webb Space Telescope. Our results highlight the critical sensitivity of galaxy assembly to the coupling between small-scale accretion physics and large-scale feedback regulation. Magnetic suppression of hot gas accretion can reconcile low-redshift constraints while preserving the rapid black hole growth required at early cosmic epochs, thereby providing a physically motivated bridge between horizon-scale GRMHD simulations and cosmological galaxy-formation models. 

Abstract Galaxies grow alongside central supermassive black holes (SMBHs) through fueling and feedback. However, the origins of this coevolution remain unclear and vary across modeling frameworks. Using semianalytic models (SAMs), we trace SMBH mass assembly acrossM_BH ∼ 10⁶⁻¹⁰M_⊙. We find significant discrepancies between observations and physics-based models of the local black hole mass function (BHMF), likely from differences in the stellar mass function and scaling relations used to infer the BHMF. Most physics-based models agree atz ∼ 1–4 and broadly match the JWST broad-line active galactic nucleus (AGN) BHMFs atz = 4–5. These models also reproduce the observed bolometric AGN luminosity evolution, except the SAMDark Sage, which predicts an excess. Interestingly, this pronounced “knee” in the bolometric AGN luminosity function predicted byDark SagearoundL_bol ∼ 10⁴⁶erg s⁻¹is consistent with the inferred abundance and luminosity of “little red dots” atz = 5–6, under the assumption that they are powered entirely by AGN activity. In contrast to other models,Dark Sagedeploys multiple growth channels for SMBHs that include mergers, hot-mode accretion, merger-driven cold-accretion, and secular-instability-driven accretion. We analyze the black hole mass buildup and accretion histories inDark Sage, which, unlike other models, also allows for super-Eddington accretion, and we find that, on average, SMBHs primarily grow through secular disk instabilities and merger-driven cold gas accretion modes. We also find that black hole mergers contribute the majority of the growth of ∼60% of the total mass budget only for the most massive SMBHs byz= 0. 

Abstract The coevolution of supermassive black holes (SMBHs) and their host galaxies remains one of the central open questions in cosmology, rooted in the coupling between accretion, feedback, and the multiscale physics that links the event horizon to the circumgalactic medium. Here we bridge these scales by embedding a first-principles, GRMHD-informed prescription for black hole accretion and feedback—derived from multizone simulations that self-consistently connect inflows and outflows from the horizon to the Bondi radius—within cosmological magnetohydrodynamic zoom-in simulations of ∼10¹⁴M_⊙halos. These GRMHD results predict a “suppressed Bondi” regime in which magnetic stresses and relativistic winds strongly reduce effective accretion rates in a spin-dependent manner. We find that black holes cannot grow efficiently by accretion until they exceed ∼10⁷M_⊙, regardless of the feedback strength. Beyond this threshold, systems bifurcate: low-spin (η ∼ 0.02) black holes continue to accrete without quenching star formation, while high-spin (η ≳ 0.3) black holes quench effectively but become starved of further growth. Early, massive seeding partially alleviates this tension through merger-driven assembly, yet an additional cold or super-Eddington accretion mode appears essential to reproduce the observed SMBH population and the empirical black hole–galaxy scaling relations. Our results demonstrate that GRMHD-informed feedback models can account for the maintenance-mode behavior of low-luminosity active galactic nuclei like M87*, but cannot by themselves explain the full buildup of SMBH mass across cosmic time. A unified, multiregime framework is required to capture the evolving interplay between spin-dependent feedback, cold inflows, and mergers in driving coevolution. 

Abstract As star-forming galaxies approach or exceed a stellar mass of around 10¹¹M_⊙, they are increasingly likely to be quenched in a process generically called mass quenching. Central galaxies, which are quenched via mass rather than environmental quenching, therefore accumulate in a peak around this characteristic mass. While a number of processes may influence the shape of the quenched central stellar mass function, we find that its low-mass slope is strongly affected by the scatter in the mass of black holes at a given stellar mass, with higher scatters in the black hole population yielding shallower slopes. Higher scatters in the black hole mass spread out the stellar mass range over which quenching occurs, leading to shallower slopes. This trend holds across a variety of semianalytic models and cosmological hydrodynamic simulations. A comparison with observations provides indirect evidence for a large scatter in black hole mass $\sigma \left({\log }_{10}\right(M_{\mathrm{BH}})\mid M_{*})\gtrsim 0.5$dex, and a joint constraint on active galactic nuclei feedback physics and the coevolution of galaxies and black holes. 

Abstract We study the coevolution of black holes (BHs) and their host galaxies in the ASTRIDandTNG300cosmological simulations and the DARKSAGEsemianalytic model (SAM), focusing on the evolution of the BH mass–stellar mass (M_BH–M_*) relation. Due to differences in the adopted subgrid modeling of BH seeding, dynamics, and feedback, the models differ in their predicted redshift evolution of theM_BH–M_*relation. We find that it is the interplay between the star formation rate (SFR) and the black hole accretion rate (BHAR) that drives the evolution of the mean relation. We define a quantity $\mathcal{R}$, the ratio between the specific BHAR and SFR (i.e., $\mathcal{R}\equiv$sBHAR/sSFR), and demonstrate that it is $\mathcal{R}$that governs the evolution of individual sources in theM_BH–M_*plane. The efficiency of BH growth versus stellar mass growth in the sSFR–sBHAR plane reflects the partitioning of gas between fueling star formation versus BH accretion. This partitioning depends on the implementation of BH dynamics and the nature of how black hole feedback quenches galaxies. In the cosmological simulations (ASTRIDandTNG300), the BHAR and SFR are intrinsically linked, resulting in a tightM_BH–M_*correlation, while the DARKSAGESAM produces a significantly larger scatter. We discuss these results in the context of recently discovered overmassive BHs and massive quenched galaxies at high redshift by the James Webb Space Telescope.