arXiv subjects

Rüdiger Pakmor

Publications and source records attributed to Rüdiger Pakmor.

At least 19 recordsLinked to original sources

arXiv2026

The inner galaxy as a window on its early assembly: lessons from a cosmological Milky Way analogue

Characterising the assembly history of the inner Milky Way is a key goal of upcoming spectroscopic surveys, yet disentangling its overlapping stellar components remains challenging. We investigate the chemodynamics of the centre of a Milky Way analogue in the Auriga Superstars cosmological hydrodynamical simulation suite, focusing on a high-resolution halo (~ 800 M_sun star particles) with a realistic galactic bar and accretion history. We classify stars within the inner 4 kpc into proto-galaxy, subsequent in-situ, and accreted components to assess their distinguishability using kinematics, dynamics, ages, and metallicities. Stellar net rotation declines sharply between [Fe/H]=0 and [Fe/H]=-1, marking the transition from disc-like in-situ stars to the proto-galaxy. While significant chemical and dynamical overlaps complicate the search for structures in energy-angular momentum (E-Lz) space, metal-poor stars ([Fe/H]<-1) at low energy form a remarkably pure (>97%) sample of proto-galaxy stars. Conversely, the high-energy, metal-poor tail offers the best chance of detecting accreted debris. However, at high energies the inner accreted halo is dominated by low-mass systems (M_star ~ 10^7 - 10^9 M _sun), not the earliest massive mergers. Dynamically, few clues remain from early mergers, and early enrichment is rapid and similar across progenitors. In-situ contamination is an issue for [Fe/H]>-1 throughout E-Lz space. Overall, while accurate stellar ages and high-precision chemical abundances may help further constrain the Milky Way's history, we should be cautious when associating stars with individual merger events in the inner galaxy.

astro-ph.GA↗

arXiv2026

Hidden Disruption in Milky Way-like Satellite Galaxy Populations

Determining whether a satellite galaxy is tidally disrupting from photometric observations alone remains a fundamental challenge in near-field cosmology. Cosmological simulations of Milky Way-mass galaxies predict that satellite populations should be highly disrupted, yet the observed Milky Way satellite population appears largely intact. Understanding this tension requires either uncovering disruption that has gone undetected in Milky Way satellites, or identifying limitations in the simulations themselves. We use the Auriga suite of cosmological simulations to evaluate several commonly used indicators of disruption. We find that, in the simulated satellite population, the shape, size, and proper motion alignment of a satellite's bound component are unreliable indicators of its present-day disruption state despite their widespread use in the literature. In contrast, the extended stellar distribution, specifically the ratio of stellar mass between $3r_{1/2}$ and $10r_{1/2}$ to that within $r_{1/2}$, is strongly correlated with disruption. We introduce the extended mass ratio $μ_{\rm EMR}$ as a metric for comparing extended stellar distributions across satellites of varying masses and exploring their connection to disruption in Milky Way observations. Applying this metric to a sample of Milky Way satellites with measured extended stellar distributions, we find that many are consistent with significant ongoing disruption, even among systems traditionally classified as intact. These results suggest that tidal disruption may be substantially more widespread in the observed Milky Way satellite population than currently recognized, and establish extended stellar distributions as a promising new tool for uncovering this hidden disruption.

astro-ph.GA↗

arXiv2026

Hierarchical Black Hole Mergers at High Redshift: Predictions for LISA and LGWA from SEEDZ

We investigate the hierarchical assembly of black holes (BHs) in the early Universe using the next-generation SEEDZ cosmological zoom-in simulations. Our suite follows two independent regions (\textsc{Rarepeak} and \textsc{Normal1}) evolved with three BH feedback prescriptions: no feedback (NoFB), weak feedback (WeakFB), and standard thermal isotropic feedback (FidBH). Focusing on BH mergers at $z \geq 10$, we explore merger-driven BH growth and detectability with next-generation gravitational-wave observatories. We find that stronger AGN feedback models dramatically suppress hierarchical BH assembly compared to weaker feedback implementations. In the NoFB simulations, BHs frequently undergo repeated mergers, with some experiencing more than 50 merger events within a few hundred Myr and gaining over $10^8,\mathrm{M_{\odot}}$ through mergers alone. In contrast, BHs in the FidBH simulations rarely undergo more than three mergers. NoFB therefore represents an upper limit to BH merger-driven growth beyond what is expected in the Universe. The suppression of BH mergers in the FidBH case is not driven by differences in galaxy assembly, BH occupation fractions, or BH seed abundances, which remain broadly similar across the simulation suites. Instead, feedback disrupts the dense gas surrounding newly formed BH seeds, suppressing their early accretion-driven growth and preventing them from entering runaway hierarchical merger pathways. Our results demonstrate that early-Universe feedback prescriptions strongly influence hierarchical BH growth through both mergers and accretion, producing distinct high-redshift merger populations. Coupled with seeding choices and other BH subgrid prescriptions, this introduces multiple degeneracies that will need to be broken in advance of LISA and other next-generation GW facilities.

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arXiv2026

Inferring magnetic field strengths in high-redshift lensing galaxies from Faraday rotation measure observations

Observations of Faraday rotation in the lensing galaxy of CLASS B1152+199 at z = 0.439 suggest that efficient dynamo mechanisms had already amplified galactic magnetic fields by this epoch. We assess the reliability of this method for deriving magnetic field strengths and the likelihood of observing similarly large Faraday rotation differences. We select 64 star-forming disk galaxies from the TNG50 cosmological magnetohydrodynamical simulation, matched to CLASS B1152+199 in mass and redshift, and forward model them using polarized radiative transfer with POLARIS and subsequent RM synthesis. TNG50 predicts characteristic large-scale field strengths of B$_0$ = 1.9-15.6 $μ$G for individual galaxies, while the combined sample yields B$_0$ = 10.3 $μ$G. Field strengths B$_{obs}$ inferred from the synthetic observations generally recover B$_0$ within a factor of three. B$_{obs}$ depends only weakly on the assumed magnetic field geometry, whereas galaxy inclination and beam depolarization have stronger effects. The differential rotation measure recovered from RM synthesis remains correlated with the directly integrated value, although beam depolarization systematically reduces its magnitude. Only 1.41% of directly integrated sightline pairs reproduce the observed $Δ$RM = 1040 $\pm$ 60 rad m$^{-2}$ of CLASS B1152+199, increasing to 3.16% for sightlines at galactocentric distances comparable to the observed 2.6 and 6.5 kpc. Differential Faraday rotation of gravitationally lensed sources therefore provides a robust probe of large-scale magnetic fields, while the large $Δ$RM of CLASS B1152+199 is relatively rare among the considered TNG50 analog galaxies.

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arXiv2026

LYRA: The formation and growth of nuclear star clusters in dwarf galaxies

Nuclear star clusters (NSCs) are dense massive star clusters ubiquitous in galactic centres across various mass regimes, present in up to $\sim30$ per cent of dwarf galaxies with $M_\star<10^{7}\, \mathrm{M}_\odot$. Although their main growth pathways are well studied, there is still ongoing debate regarding their formation. We use the LYRA cosmological hydrodynamical simulations to study the formation and growth of NSCs in a sample of six dwarf galaxies, where we identify NSCs with masses $M_\mathrm{NSC} \sim 10^4 - 10^6 \, \mathrm{M}_\odot$ in all galaxies in our sample. The NSCs in our sample emerge at early times as a compact component, with the host galaxy growing around them. This is consistent with a scenario in which NSCs are among the earliest structures to form in a galaxy. We characterise the origin of the stars that constitute the NSCs and explore the properties of the stellar populations in each of these channels. We find that most of the NSC mass originates from in-situ star formation within the NSCs themselves. While this might appear at odds with current observations, the bulk of this star formation occurs at early times, resulting in a significant population of old and metal-poor stars, in agreement with an early NSC formation. We also identify galaxy-galaxy mergers as a significant contributor to the NSC mass, with usually one merger dominating this contribution. Our results highlight the complexity in the growth history of NSCs in dwarf galaxies and highlight the importance of considering additional growth channels for NSCs in dwarfs galaxies.

astro-ph.GA↗

arXiv2026

Divergence-free magnetohydrodynamics on a moving mesh

Magnetic fields are ubiquitous in the Universe and play an important role in many astrophysical processes, such as star formation and the evolution of galaxies. Hydrodynamical simulation methods that account for ideal magnetohydrodynamics (MHD) are however challenged by the need to achieve numerical stability and physical consistency. Both can be compromised by the occurrence of non-vanishing local divergence errors in the magnetic field. Different approaches to either eliminate or reduce these discretization errors are in widespread use, including constrained transport or divergence cleaning techniques. However, thus far a divergence-free Galilean invariant formulation of MHD that can be readily applied in Lagrangian codes has been an elusive goal. Here we revisit the use of the vector potential for evolving the magnetic field on an unstructured moving-mesh and show how a particular gauge choice combined with a suitably discretized integration scheme provides a stable and accurate formulation of MHD. Our method combines a finite-difference evolution of a cell-centred vector potential with a finite volume representation of the other fluid quantities, and is realized in the moving-mesh code AREPO. The new approach is fully Galilean invariant and therefore shows vanishing errors for classic problems such as field loop advection. We demonstrate good accuracy and stability when our scheme is applied to various test problems and to practical applications in 3D, including when local timesteps and adaptive mesh refinement and derefinement are used.

astro-ph.IM↗

arXiv2026

The Entangling of Supernova Feedback Impacts with Coarsening Simulation Resolution

It is often understood that supernova (SN) feedback in galaxies is responsible for regulating star formation (SF) and generating gaseous outflows. However, a detailed look at the small-scale effects of SNe on the interstellar medium (ISM) in simulations shows that the macroscopic processes of SF suppression and outflow generation proceed in distinct channels. We demonstrate this finding in two independent simulations of isolated dwarf galaxies with very high (m_gas ~ Msun) numerical resolution, LYRA and RIGEL. Our findings suggest that the macroscopic effect of a given SN on the galaxy is best predicted by its local density. Outflows are driven by SNe in diffuse regions expanding to their cooling radii on large (~kpc) scales, while dense SF regions are disrupted in a localized (~pc) manner. However, these separate feedback channels are only distinguishable at very high resolutions capable of following mass scales \lesssim 10^2 \msun. When averaging on coarser scales, ISM densities are greatly mis-estimated, and variations between different SF and SNe-affected regions are severely washed out. It therefore cannot be __self-consistently__ determined, from coarse-resolution information __alone__, (1) whether a SN tends to contribute to outflows or direct SF suppression, and (2) the rate of SF in a given region. In particular, commonly used parameters in coarse-resolution (subgrid) models, such as the SN cooling radius and SF density threshold, may require more detailed treatments informed by high-resolution studies.

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arXiv2026

Same galaxy, different CGM: how the metal loading of galactic winds regulates the baryon cycle in Milky Way-mass galaxies

The circumgalactic medium (CGM) is both the reservoir of gas that fuels star formation and galaxy growth, and the repository for the mass, energy, and metals expelled through stellar evolution and feedback. We present a controlled experiment using a suite of five cosmological magnetohydrodynamical simulations of a Milky Way-mass halo from the Auriga suite, where we vary the metal content and energy loading of galactic winds driven by stellar feedback. We chose these parameters in combination such that all five runs obtain very similar (within $\approx$10\%) $z=0$ stellar masses and morphologies and thus produce similar amounts of metals throughout their lifetimes. Our simulations differ substantially in where these metals end up, spatially within the halo and across the different baryonic components (stars, gas disc, CGM, and the intergalactic medium). The metal content affects the cooling efficiency of the halo gas, regulating the CGM cool gas fraction and the accretion rates onto the galaxy. Between our two extreme models, we report an order of magnitude difference in the median gas metallicity at vertical heights $|z| \gtrsim 30$ kpc above the disc plane. Current constraints on the metallicity of the Milky Way halo gas from absorption-line measurements of intermediate- and high-velocity clouds at $|z| \lesssim 15$ kpc are broadly consistent with our simulations, though a direct comparison is limited by differences in the adopted methods. Our findings show that galaxies with nearly identical stellar content and morphology can differ substantially in their CGM, which offers a promising avenue for constraining feedback physics within galaxy formation models.

astro-ph.GA↗

arXiv2026

JWST Spectroscopy of Type Ia Supernova 2025rbs from Maximum Light to the Nebular Phase

We present JWST observations of the Type Ia supernova (SN Ia) 2025rbs ($D=$14.5 Mpc) at +1, +23, and +84 days after B-band maximum, spanning peak light through a wavelength-dependent transition toward the nebular phase. Combined with ground-based optical and near-infrared (NIR) data, our panchromatic spectra (0.4-14 $μ$m) include the first maximum-light mid-infrared (MIR) spectrum and the earliest MIR spectroscopic sequence of an SN Ia to date. At peak light, the MIR spectrum exhibits a continuum with permitted and forbidden features, including Si II, Ni II, and early-emerging [Ni III-IV] and [Ar II-III]. By +23 days the MIR is dominated by forbidden lines with a weak continuum, and by +84 days it is fully nebular, whereas the optical/NIR spectra remain transitional. The nebular spectrum reveals strongly stratified ejecta, with stable Ni concentrated at the lowest velocities, radioactive Co at intermediate velocities but absent within ~2000 km s$^{-1}$, and Ar occupying an outer shell. We detect small-scale substructure in [Ca IV] 3.21 $μ$m with fractional amplitudes of a few percent and a characteristic velocity scale of ~800 km s$^{-1}$, which may reflect compositional structure, ionization variations, or both. Radiative-transfer calculations substantially underpredict these MIR Mg II features despite approximately reproducing the NIR Mg II 1.0927 $μ$m line, suggesting that the relative strengths of these transitions are sensitive to the treatment of Mg ionization and excitation. These observations demonstrate that MIR spectroscopy beginning near maximum light simultaneously probes the emerging inner ejecta and rapidly fading outer burning products, providing new constraints for explosion and radiative-transfer models.

astro-ph.HE↗

arXiv2026

Introducing the Lumina project: large-volume radiation-hydrodynamic simulations of the epochs of hydrogen and helium reionization

Understanding how galaxies and active galactic nuclei (AGN) jointly drive the reionization of the intergalactic medium (IGM) across cosmic time remains a major challenge in cosmology. We present Lumina, a large-volume radiation-hydrodynamic simulation that self-consistently follows the coupled evolution of the intergalactic medium, galaxies, and AGN through HI, HeI, and HeII reionization down to redshift $z=3$. Lumina evolves a cosmological volume of comoving side length $L_{\mathrm{box}}=500\,\mathrm{cMpc}$ with $2\times 6000^{3}$ resolution elements, corresponding to baryonic and dark-matter mass resolutions of $3.6\times 10^{6}\,\text{M}_{\odot}$ and $1.9\times 10^{7}\,\text{M}_{\odot}$, respectively. The simulation uses the moving-mesh code AREPO, combining the IllustrisTNG galaxy-formation model with a GPU-accelerated M1 radiation-transport solver in six frequency bins. The initial conditions employ separate transfer functions for baryons and dark matter and include their relative streaming velocity. Lumina predicts a late, predominantly stellar-driven hydrogen reionization, with the median sub-volume fully ionized by $z\approx 5.2$ and residual neutral HI patches persisting until $z\approx 4.75$. HeII reionization is driven self-consistently by AGN and is nearly complete by $z=3$. The simulation yields a Thomson-scattering optical depth in excellent agreement with Planck, an IGM thermal history and photoionization background broadly consistent with observational constraints, and a clear late-time thermal boost associated with HeII reionization. Its galaxy population remains consistent with the original IllustrisTNG project, while the larger volume improves statistics for rare objects, large-scale environments, and cosmic variance, enabling forward modelling of observables linking HI and HeII topologies to the evolving galaxy and AGN populations.

astro-ph.CO↗

arXiv2026

A comparison of numerical schemes for driven subsonic MHD turbulence

Turbulence is ubiquitous in astrophysical systems, and since most cosmic gas is ionised, it supports magnetic fields. In turbulent environments, these fields are rapidly amplified through a small-scale dynamo. Multi-scale astrophysical simulations, however, rarely resolve this process adequately. Limited spatial dynamic range makes small-scale amplification sensitive to the numerical choices made in the hydrodynamics and magnetic field solvers. Here, we investigate idealised periodic boxes of driven subsonic turbulence with a weak seed magnetic field. These simulations with purely numerical dissipation provide a simple environment in which an efficient small-scale dynamo is expected. We aim to systematically compare the three widely used magnetohydrodynamics (MHD) codes \textsc{Arepo}, \textsc{Athena}, and \textsc{Ramses} across different divergence-control schemes: constrained transport, Powell cleaning, and Dedner cleaning. To minimise comparison bias, we adopt identical turbulent driving and analysis pipelines across all runs. At sufficient resolution, every code and scheme we test exhibits dynamo-like exponential amplification of the seed field until saturation. The structural properties of the magnetic field in both the kinematic and saturated regimes are consistent across schemes (with the exception of \textsc{Arepo}'s constrained transport) and agree with theoretical expectations. Residual differences, particularly in kinematic amplification rates and saturation strengths at fixed resolution, appear attributable to varying levels of numerical diffusion. Notably, we find for this setup no systematic advantage of constrained transport over divergence-cleaning methods. We stress that this comparison, conducted in a highly idealised setting, represents a first step. Future extensions to more complex and physically realistic configurations remain essential.

astro-ph.IM↗

arXiv2026

SEEDZ: Rapid Galaxy Assembly as a Pathway to Supermassive Stars, Dense Stellar Environments and Massive Black Hole Seeds

We investigate the assembly history of early galaxies in the SEEDZ hydrodynamic simulations, to investigate the high inflow rates believed to be required for the formation of supermassive stars (SMSs), dense stellar clusters and subsequently heavy seed black holes. Using a heavy seed formation criteria of $>$1 M$_\odot$ yr$^{-1}$ flowing into 10 pc regions, we find that heavy seeds form in halos that grow rapidly compared to those halos that never meet the criteria. Halos with growth rates of $\gtrsim$1 M$_\odot$ yr$^{-1}$ at their virial radius (scales of a few hundred pc) are able to sustain a flow rate of 0.1 M$_\odot$ yr$^{-1}$ into the inner 1 pc of the halo, maintaining higher density environments within the central 10 - 100~pc. These halos continue to grow rapidly after their initial collapse, typically forming heavy seeds $\sim$100 Myr after forming their first stars and stellar mass black holes. By $z=10$, most heavy seeds form in regions of near-solar metallicity, although a minority of heavy seeds do continue to form in low metallicity (10$^{-2}$ Z$_\odot$) regions. Under the assumption that a SMS forms as the progenitor to a heavy seed if it forms in a region of low (10$^{-2}$ Z$_\odot$) metallicity, and can sustain high accretion rates above 0.02 M$_\odot$ yr$^{-1}$ throughout the SMS lifetime of 2 Myr, we find a number density of SMSs of 0.1 cMpc$^{-3}$, meaning that only a fraction of 10$^{-4}$ of these SMSs would need to be visible to JWST to account for the observed population of Little Red Dot galaxies.

astro-ph.GA↗

arXiv2026

Active galactic nucleus driven jet feedback in cosmologically forming cool-core galaxy clusters I: The effect of hierarchical assembly on intra-cluster medium properties

The atmospheres of cool-core galaxy clusters are excellent probes of astrophysical plasmas. However, how the interplay between assembly and active galactic nucleus (AGN) feedback leads to the observed gas profiles remains uncertain. We study the impact of hierarchical assembly on the intra-cluster medium (ICM) in cool-core galaxy clusters using hydrodynamic simulations as part of the PICO-Cluster project. We compare cosmological zoom simulations employing an explicit AGN jet model against PICO-Cluster simulations with IllustrisTNG kinetic AGN feedback, as well as against isolated galaxy cluster simulations using jet feedback. The stellar and gas fractions of our cosmological galaxy cluster simulations with jet feedback are in excellent agreement with observed galaxy clusters, and the ICM thermodynamic profiles resemble those of local cool-core galaxy clusters while those run with IllustrisTNG kinetic AGN feedback do not match these observations. In all simulations, cosmological and isolated, the AGN heating roughly balances the cooling losses, with star formation being significantly suppressed. The most notable differences between the cosmological and isolated simulations are the resulting velocity and multi-phase structure: gas at radii $> 50$ kpc is shaped by satellite galaxies rather than jet feedback originating form the central galaxy. This leads to significant differences in non-thermal pressure support, with only the cosmological simulations being consistent with recent observations. A second notable difference is the abundance of warm ($<10^5$ K) gas beyond the core region, which is absent in our isolated simulation. Our results highlight the need for taking cosmological assembly into account in comparisons of the ICM dynamics and its multi-phase nature, while self-regulation is altered by hierarchical assembly via merger-driven growth of the central supermassive black hole.

astro-ph.GA↗

arXiv2026

The PICO-Cluster Project: presenting the galaxy cluster sample and studying magnetic field growth, Faraday rotation and Braginskii heating

Galaxy clusters constitute a microcosm of the Universe and offer a unique laboratory for studying plasma astrophysics, encompassing processes such as cosmic-ray acceleration and non-thermal radio emission, turbulence, weakly collisional plasma physics, and transformative mechanisms in galaxy evolution. To investigate these phenomena, we introduce the PICO-Cluster project, studying 'Plasmas In COsmological Clusters' using a suite of high-resolution cosmological zoom-in simulations of massive galaxy clusters with masses $\gtrsim10^{15}$M$_\odot$ selected from a parent simulation box with a comoving side length of 1 $h^{-1}$Gpc. In this work, we present 24 baseline simulations performed with the moving-mesh AREPO code and the IllustrisTNG galaxy formation model, achieving a baryonic mass resolution of up to $1.4\times10^{6}\mathrm{M}_\odot$. The initial conditions are carefully designed to exclude low-resolution particle contamination within the high-resolution region; as a result, all clusters remain free of such contamination out to at least 2.7 $R_{200}$ at all times. Our galaxy and cluster properties agree with recent simulations and many observational constraints, including scaling relations and thermodynamic profiles. The magnetic energy within the cluster is numerically converged once the small-scale dynamo has saturated, yielding a remarkably tight volume-averaged plasma-beta of $β\approx100$ inside $R_{200}$ across our sample after redshift $z\sim1.2$. Faraday rotation measure profiles, which trace the line-of-sight magnetic field and electron density, decline with cylindrical radius; notably, the mean decreases more rapidly than the root-mean-square due to the increasing relative contribution of galaxies at larger radii. Finally, viscous heating rates in Braginskii theory are highly intermittent and, on average, approach radiative cooling rates in the cluster outskirts.

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arXiv2026

X-ray emission maps and scaling relations in IllustrisTNG and MillenniumTNG: Differences between cluster and group regimes

X-ray observations are a primary probe of the intracluster medium, widely used to infer galaxy cluster masses and scaling relations. We present and validate a pipeline to generate X-ray emission maps of galaxy groups and clusters from large cosmological simulations, and use it to study the origin of deviations from self-similarity across the group-to-cluster transition. We apply this pipeline to the Illustris-TNG300 and MillenniumTNG simulations, constructing \mbox{X-ray} emission maps and spectra based on APEC cooling functions. For simulations that do not explicitly track individual chemical abundances, we introduce a metallicity-based prescription that accurately reproduces the full spectral emission. We derive the $L_{\mathrm{X}}$--$M_{500}$, $M_{\mathrm{gas}}$--$M_{500}$, and $T$--$M_{500}$ scaling relations over $10^{12.5} \leq M_{500} \leq 10^{15.5}\,\mathrm{M}_\odot$, compare them with observational data, and quantify the hydrostatic equilibrium and spectroscopic temperature biases through synthetic X-ray analyses. The simulated scaling relations are in good overall agreement with observations and are best described by broken power laws with a pivot at $M_{500}=10^{13.67}\,\mathrm{M}_\odot$. At high masses, the slopes are close to self-similar expectations; at lower masses the relations steepen significantly, reflecting the growing importance of AGN feedback. X-ray hydrostatic masses are systematically underestimated by $15\%$, independently of cluster mass. When spectroscopic effects are included, the bias becomes mass-dependent, ranging from $15\%$ at low masses to $21\%$ at high masses. The recovered X-ray luminosity, measured in the $0.15$--$1\,R_{500}$ aperture, is also mass-dependent: high-mass clusters are underestimated by $18\%$, while low-mass systems show discrepancies of up to $33\%$, driven by single-temperature spectral modelling of the gas outside the core.

astro-ph.GA↗

arXiv2026

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$_\odot$.

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arXiv2026

JWST Spectroscopy of SN Ia 2022aaiq and 2024gy: Evidence for Enhanced Central Stable Ni Abundance and a Deflagration-to-Detonation Transition

We present optical + near-infrared (NIR) + mid-infrared (MIR) observations of the normal Type Ia supernovae (SN Ia) 2022aaiq and 2024gy in the nebular phase, continuously spanning 0.35-28 microns. Medium-resolution JWST spectroscopy reveals novel narrow ($v_{\mathrm{FWHM}}<1500$ km s$^{-1}$) [Ni II] 1.94 and 6.64 micron cores in both events. The MIR [Ni II] 6.64 micron line exhibits a distinct narrow core atop a broader base, indicating a central enhancement of stable Ni. This structure points to high central densities consistent with a near-Chandrasekhar-mass ($M_{\text{Ch}}$) progenitor or a high-metallicity sub-$M_{\text{Ch}}$ progenitor. From detailed line-profile inversions of SN 2024gy, we derive emissivity profiles for stable iron-group elements (IGEs), radioactive material, and intermediate-mass elements (IMEs), revealing spatially distinct ejecta zones. The [Ni III] 7.35 micron line shows a shallow-to-steep slope transition - a "broken-slope" morphology - that matches predictions for delayed detonation explosions with separated deflagration and detonation ashes. We also reanalyze and compare to archival JWST spectra of SN 2021aefx and the subluminous SN 2022xkq. From the stable Ni luminosities, we infer that SN 2024gy produced ~5-10 times more stable Ni mass than SN 2022xkq, favoring a near-$M_{\text{Ch}}$ scenario for SN 2024gy and sub-$M_{\text{Ch}}$ scenario for SN 2022xkq. These results demonstrate that resolved line profiles, now accessible with JWST, provide powerful diagnostics of explosion geometry, central density, and progenitor mass in SN Ia.

astro-ph.HE↗

arXiv2026

Learning the Universe: Constrained simulations of the Coma galaxy cluster -- I. Radial X-ray and Compton-y signatures

We present a suite of 50 high-fidelity simulations of Coma cluster analogues constructed from BORG/MANTICORE constrained initial conditions and evolved with the IllustrisTNG galaxy formation model. Regions predicted to form massive clusters comparable to Coma in mass and environment are selected and followed through cosmic time, producing realistic galaxy populations and intracluster medium properties. The ensemble captures both cosmic variance and uncertainties in the local initial conditions, providing a statistically robust framework for interpreting Coma in a cosmological context. We focus on direct comparisons with observed thermodynamical profiles of the intracluster medium. Specifically, we extract X-ray surface brightness profiles from the simulated clusters and confront them with measurements from eROSITA, as well as compute the thermal Sunyaev--Zel'dovich effect via integrated Compton-$y$ profiles for comparison with Planck satellite data. The simulations reproduce the broad shape and normalisation of both observables, while also highlighting the range of scatter expected from environmental and assembly history differences. This enables us to assess how feedback processes, merger activity, and large-scale environment shape observable cluster properties. Our results demonstrate that combining constrained cosmological initial conditions with state-of-the-art galaxy formation physics provides an effective strategy for generating targeted, observation-driven analogues of specific clusters. The resulting dataset offers a valuable resource for testing models of intracluster medium physics, calibrating scaling relations, and interpreting upcoming joint X-ray and Sunyaev--Zel'dovich observations of nearby massive clusters.

astro-ph.CO↗