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Abstract We present a novel method for systematically assessing the impact of the central potential fluctuations associated with bursty outflows on the structures of dark matter halos for classical and ultrafaint dwarf (UFD) galaxies. Specifically, we use dark-matter-only simulations augmented with a manually added massive particle that modifies the central potential and approximately accounts for a centrally concentrated baryonic component. This approach enables precise control over the magnitude, frequency, and timing of rapid outflow events. We demonstrate that this method can reproduce the established result of core formation for systems that undergo multiple episodes of bursty outflows. In contrast, we also find that equivalent models involving only single (or a small number of) burst episodes do not form cores with the same efficacy. This is important because many UFDs in the local Universe are observed to have tightly constrained star formation histories that are best described by a single early burst of star formation. Using a suite of cosmological zoom-in simulations, we identify the regimes in which single bursts can and cannot form a cored density profile. Our results suggest that it may be difficult to form cores in UFD-mass systems with a single early burst, regardless of its magnitude. 

ABSTRACT We study fast nuclear winds driven by active galactic nucleus (AGN) feedback in merging galaxies using high-resolution hydrodynamics simulations. We use Stars and MUltiphase Gas in GaLaxiEs (smuggle) to explicitly model the multiphase interstellar medium (ISM) and employ subgrid dynamical friction for massive black holes (BHs). Furthermore, we use a super-Lagrangian refinement scheme to resolve AGN feedback coupling to the ISM at $$\sim 10-100\,$$ pc scales. By comparison between merging and isolated galaxies, with and without AGN feedback, we identify trends in the complex interplay between dynamics, BH fuelling and feedback, and star formation and feedback. We consider three galaxy types: Milky Way analogues, Sbc-type galaxies, and Small Magellanic Cloud (SMC) analogues. The synergy between AGN feedback and merger dynamics is strongest in the Milky Way-like mergers, where the AGN winds are energetically dominant and entrain more gas when the initially thin discs become thick and amorphous during the merger. In contrast, the merger of thicker, vigorously star-forming Sbc galaxies is not strongly impacted by AGN feedback until star formation declines in the post-merger phase. Finally, while the subgrid dynamical friction prescription effectively retains BHs in galactic nuclei during more massive mergers, the clumpy multiphase ISM induces significant wandering of low-mass BHs $$\mathrm{(< 10^5\, M_\odot)}$$ in the shallow potentials of the SMC-like galaxies. These low-mass BHs wander at distances $$\gtrsim 2$$ kpc from the galactic centre, yielding negligible BH accretion and feedback. This has implications for Laser Interferometer Space Antenna event rates and present a further challenge to understanding the rapid growth of $$z\sim 7-10$$ quasars discovered by James Webb Space Telescope. 

ABSTRACT We present an investigation into the quenching of simulated galaxies across cosmic time, honing in on the role played by both intrinsic and environmental mechanisms at different epochs. In anticipation of VLT-MOONRISE, Very Large Telescope MOONS (Multi-Object Optical and Near-infrared Spectrograph) Redshift-Intensive Survey Experiment, the first wide-field spectroscopic galaxy survey to target cosmic noon, this work provides clear predictions to compare to the future observations. We investigate the quenching of centrals, high-mass satellites, and low-mass satellites from two cosmological hydrodynamical simulations: Illustris The Next Generation and Evolution and Assembly of GaLaxies and their Environment. Satellites are split according to bespoke mass thresholds, designed to separate environmental and intrinsic quenching mechanisms. To determine the best parameter for predicting quiescence, we apply a Random Forest classification analysis for each galaxy class at each epoch. The Random Forest classification determines supermassive black hole mass as the best predictor of quiescence in centrals and high-mass satellites. Alternatively, the quenching of low-mass satellites is best predicted by group halo mass, at all epochs. Additionally, we investigate the evolution in the dependence of the quenched fraction with various parameters, revealing a more complex picture. There is strong evidence for the rejuvenation of star formation from z = 2 to z = 0 in EAGLE, but not in IllustrisTNG. The starkest discrepancy between simulations rests in the mass threshold analysis. While IllustrisTNG predicts the existence of environmentally quenched satellites visible within the survey limits of MOONRISE, EAGLE does not. Hence, MOONRISE will provide critical data that is needed to evaluate current models, and constrain future models, of quenching processes. 

Abstract From the luminous quasars atz∼ 6 to the recentz∼ 9–11 active galactic nuclei (AGN) revealed by JWST, observations of the earliest black hole (BH) populations can provide unique constraints on BH evolution. We use theBRAHMAsimulations with constrained initial conditions to investigate BH assembly in extreme overdense regions. The simulations implement heavy ∼10⁴–10⁵M_⊙seeds forming in dense, metal-poor gas exposed to sufficient Lyman–Werner flux. With gas accretion modeled via the Bondi–Hoyle formalism and BH dynamics with a subgrid dynamical friction scheme, we isolate the impact of seeding, dynamics, accretion, and feedback on BH evolution. With fiducial stellar and AGN feedback inherited fromIllustrisTNG, accretion is suppressed atz≳ 9, leaving mergers as the dominant growth channel. Gas accretion dominates atz≲ 9, where permissive models (super-Eddington or low radiative efficiency) build ∼10⁹M_⊙BHs powering quasars byz∼ 6, while stricterIllustrisTNG-based prescriptions yield much smaller BHs (∼10⁶–10⁸M_⊙). Our seed models strongly affect mergers atz≳ 9: only the most lenient models (with ∼10⁵M_⊙seeds) produce enough BH mergers to reach ≳10⁶M_⊙byz∼ 10, consistent with current estimates for GN-z11. Our dynamical friction model gives low merger efficiencies. Therefore, even in such extreme regions, we are unable to produce ≳10⁷M_⊙BHs byz∼ 9–10, as currently inferred for GHZ9, UHZ1, and CAPERS-LRD-z9. If the BH-to-stellar mass ratios of these sources are indeed so extreme, they would require either very short BH merger timescales or reduced AGN thermal feedback. Weaker stellar feedback boosts both star formation and BH accretion and cannot raise these ratios. 

Abstract Integral field units have extended our knowledge of galactic properties to kiloparsec (or, sometimes, even smaller) patches of galaxies. These scales are where the physics driving galaxy evolution (feedback, chemical enrichment, etc.) take place. Quantifying the spatially resolved properties of galaxies, both observationally and theoretically, is therefore critical to our understanding of galaxy evolution. To this end, we investigate spatially resolved scaling relations within galaxies ofM_⋆ > 10^9.0atz= 0 in IllustrisTNG. We examine both the resolved star formation main sequence (rSFMS) and the resolved mass–metallicity relation (rMZR) using 1 kpc × 1 kpc maps. We find that the rSFMS in IllustrisTNG is well described by a power law but is significantly shallower than the observed rSFMS. However, the disagreement between the rSFMS of IllustrisTNG and observations is likely driven by an overestimation of AGN feedback in IllustrisTNG for the higher-mass hosts. Conversely, the rMZR for IllustrisTNG has very good agreement with observations. Furthermore, we argue that the rSFMS is an indirect result of the Schmidt–Kennicutt law and local gas relation, which are both independent of host galaxy properties. Finally, we expand upon a localized leaky-box model to study the evolution of idealized spaxels and find that it provides a good description of these resolved relations. The degree of agreement, however, between idealized spaxels and simulated spaxels depends on the “net” outflow rate for the spaxel, and the IllustrisTNG scaling relations indicate a preference for a low net outflow rate. 

Abstract We analyze the dynamics of low-mass black hole (BH) seeds in the high-redshift (z ≳ 5) Universe using a suite of [4.5 Mpc]³and [9 Mpc]³BRAHMAcosmological hydrodynamic simulations. The simulations form seeds with massM_seed = 2.2 × 10³M_⊙in halos that exceed critical thresholds of dense and metal-poor gas mass (5–150M_seed) and the halo mass (1000–10,000M_seed). While the initialBRAHMAboxes pinned the BHs to the halo centers, here we implement a subgrid dynamical friction (DF) model. We also compare simulations where the BH is allowed to wander without the added DF. We investigate the spatial and velocity offsets of BHs in their host subhalos, as well as BH merger rates. We find that subgrid DF is crucial to ensure that a significant fraction of BHs effectively sink to halo centers byz ∼ 5, thereby enabling them to get gravitationally bound and merge with other BHs at separations close to the spatial resolution (∼0.2–0.4 kpc) of the simulation. For the BHs that merge, the associated merger timescales lag between ∼100 and 1000 Myr after their host halos merge. Compared to predictions using BH repositioning, the overallz ≳ 5 BH merger rates under subgrid DF decrease by a factor of ∼4–10. Under subgrid DF, the different seed models predict merger rates between ∼100 and 1000 events per year atz ≳ 5. These mergers dominate early BH growth, assembling BHs up to ∼10⁴–10⁵M_⊙byz ∼ 5, wherein ≲2% of their mass is assembled via gas accretion. Our results highlight the promise for constraining seeding mechanisms using gravitational waves from future facilities such as the Laser Interferometer Space Antenna. 

Abstract The merger timescales of isolated low-mass pairs (10⁸<M_*< 5 × 10⁹M_⊙) on cosmologically motivated orbits have not yet been studied in detail, though isolated high-mass pairs (5 × 10⁹<M_*< 10¹¹M_⊙) have been studied extensively. It is common to apply the same separation criteria and expected merger timescales of high-mass pairs to low-mass systems, however, it is unclear if their merger timescales are similar, or if they evolve similarly with redshift. We use the Illustris TNG100 simulation to quantify the merger timescales of isolated low-mass and high-mass major pairs as a function of cosmic time, and explore how different selection criteria impact the mass and redshift dependence of merger timescales. In particular, we present a physically motivated framework for selecting pairs via a scaled separation criterion, wherein pair separations are scaled by the virial radius of the primary’s Friends-of-Friends (FoF) group halo (r_sep< 1R_vir). Applying these scaled separation criteria yields equivalent merger timescales for both mass scales at all redshifts. Alternatively, static physical separation selections applied equivalently to all galaxy pairs at all redshifts lead to a difference in merger rate of up to ∼1 Gyr between low- and high-mass pairs, particularly forr_sep< 150 kpc. As a result, applying the same merger timescales to physical-separation-selected pairs will lead to a bias that systematically overpredicts low-mass galaxy merger rates. 

ABSTRACT The origin of the ‘seeds’ of supermassive black holes (BHs) continues to be a puzzle, as it is currently unclear if the imprints of early seed formation could survive to today. We examine the signatures of seeding in the local Universe using five $$[18~\mathrm{Mpc}]^3$$BRAHMA simulation boxes run to $z=0$. They initialize $$1.5\times 10^5~\rm {M}_{\odot }$$ BHs using different seeding models. The first four boxes initialize BHs as heavy seeds using criteria that depend on dense and metal-poor gas, Lyman–Werner radiation, gas spin, and environmental richness. The fifth box initializes BHs as descendants of lower mass seeds ($$\sim 10^3~\rm {M}_{\odot }$$) using a new stochastic seed model built in our previous work. In our simulations, we find that the abundances and properties of $$\sim 10^5-10^6~\rm {M}_{\odot }$$ local BHs hosted in $$M_*\lesssim 10^{9}~\rm {M}_{\odot }$$ dwarf galaxies, are sensitive to the assumed seeding criteria. This is for two reasons: (1) there is a substantial population of local $$\sim 10^5~\rm {M}_{\odot }$$ BHs that are ungrown relics of early seeds from $$z\sim 5-10$$; (2) BH growth up to $$\sim 10^6~\rm {M}_{\odot }$$ is dominated by mergers in our simulations all the way down to $$z\sim 0$$. As the contribution from gas accretion increases, the signatures of seeding start to weaken in more massive $$\gtrsim 10^6~\rm {M}_{\odot }$$ BHs, and they are erased for $$\gtrsim 10^7~\rm {M}_{\odot }$$ BHs. The different seed models explored here predict abundances of local $$\sim 10^6~\rm {M}_{\odot }$$ BHs ranging from $$\sim 0.01-0.05~\mathrm{Mpc}^{-3}$$ with occupation fractions of $$\sim 20-100~{{\ \rm per\ cent}}$$ for $$M_*\sim 10^{9}~\rm {M}_{\odot }$$ galaxies. These results highlight the potential for placing constraints on seeding models using local $$\sim 10^5-10^6~\rm {M}_{\odot }$$ BHs hosted in dwarf galaxies. Since merger dynamics and accretion physics impact the persistence of seeding signatures, and both high and low mass seed models can produce similar local BH populations, disentangling their roles will require combining high and low redshift constraints. 

Abstract Simulations of galaxy formation are mostly unable to resolve the energy-conserving phase of individual supernova events, having to resort to subgrid models to distribute the energy and momentum resulting from stellar feedback. However, the properties of these simulated galaxies, including the morphology, stellar mass formed, and the burstiness of the star formation history, are highly sensitive to the numerical choices adopted in these subgrid models. Using the SMUGGLE stellar feedback model, we carry out idealized simulations of anM_vir∼ 10¹⁰M_⊙dwarf galaxy, a regime where most simulation codes predict significant burstiness in star formation, resulting in strong gas flows that lead to the formation of dark matter cores. We find that by varying only the directional distribution of momentum imparted from supernovae to the surrounding gas, while holding the total momentum per supernova constant, bursty star formation may be amplified or completely suppressed, and the total stellar mass formed can vary by as much as a factor of ∼3. In particular, when momentum is primarily directed perpendicular to the gas disk, less bursty and lower overall star formation rates result, yielding less gas turbulence, more disky morphologies, and a retention of cuspy dark matter density profiles. An improved understanding of the nonlinear coupling of stellar feedback into inhomogeneous gaseous media is thus needed to make robust predictions for stellar morphologies and dark matter core formation in dwarfs independent of uncertain numerical choices in the baryonic treatment. 

ABSTRACT JWST has revealed a large population of accreting black holes (BHs) in the early Universe. Recent work has shown that even after accounting for possible systematic biases, the high-z$$M_*{\!-\!}M_{\rm \rm bh}$$ relation can be above the local scaling relation by $$\gt 3\sigma$$. To understand the implications of these overmassive high-z BHs, we study the BH growth at $$z\sim 4{\!-\!}7$$ using the $$[18~\mathrm{Mpc}]^3$$BRAHMA cosmological simulations with systematic variations of heavy seed models that emulate direct collapse black hole (DCBH) formation. In our least restrictive seed model, we place $$\sim 10^5~{\rm M}_{\odot }$$ seeds in haloes with sufficient dense and metal-poor gas. To model conditions for direct collapse, we impose additional criteria based on a minimum Lyman Werner flux (LW flux $$=10~J_{21}$$), maximum gas spin, and an environmental richness criterion. The high-z BH growth in our simulations is merger dominated, with a relatively small contribution from gas accretion. The simulation that includes all the above seeding criteria fails to reproduce an overmassive high-z$$M_*{\!-\!}M_{\rm bh}$$ relation consistent with observations (by factor of $$\sim 10$$ at $$z\sim 4$$). However, more optimistic models that exclude the spin and environment based criteria are able to reproduce the observed relations if we assume $$\lesssim 750~\mathrm{Myr}$$ delay times between host galaxy mergers and subsequent BH mergers. Overall, our results suggest that current JWST observations may be explained with heavy seeding channels if their formation is more efficient than currently assumed DCBH conditions. Alternatively, we may need higher initial seed masses, additional contributions from lighter seeds to BH mergers, and / or more efficient modes for BH accretion.