arXiv subjects

Ulrich P. Steinwandel

Publications and source records attributed to Ulrich P. Steinwandel.

At least 19 recordsLinked to original sources

arXiv2026

The OpenGadget3 Code for Cosmological Simulations

We present the public release of OpenGadget3 (OG3), a substantially extended and re-organised version of the widely used Gadget-2/3 family of cosmological simulation codes. Since G2 was made publicly available, the absence of continued official development led to the creation of numerous, mutually incompatible developer versions of G3 across the community. This made it effectively impossible to track bug fixes, reproduce published results, or consistently credit the many individual contributors. OG3 addresses this by consolidating these disparate developments into a single, documented, and continuously maintained code base, released under the GNU GPLv3 through a GitLab repository (with an accompanying wiki), regularly synchronised with the active developer branch, and supported by a dedicated continuous-integration (CI) pipeline. OG3 retains the core algorithmic backbone of its predecessors, a Barnes\&Hut oct-tree combined with a Particle-Mesh method for gravity, and a choice of Smoothed Particle Hydrodynamics or Meshless-Finite-Mass solvers for gas dynamics, within a hybrid MPI/OpenMP parallelisation framework, extended with GPU offloading via OpenACC and OpenMP. The code integrates an extensive suite of sub-resolution and physical modules, including primordial chemistry, radiative cooling, star formation, stellar feedback and chemical enrichment, dust formation and evolution, black hole growth and AGN feedback, MHD, thermal conduction, physical viscosity, SIDM, and massive neutrinos. OG3 introduces new features improving robustness, reproducibility, and usability: a flexible mixed-precision framework spanning 16- to 128-bit representations; expert-level tagged parameters with restart-time change log; extensive consistency checks against invalid configurations; and FAIR-compliant reporting of all settings, parameters, and specific publications. (shortened and abridged)

astro-ph.IM↗

arXiv2026

Simulating the LOcal Web (SLOW) -- VI: Gamma-ray Emission in the Local Universe

Context: Diffuse $γ$-ray emission from cosmic-ray (CR) protons scattering off the gas in the intracluster and intergalactic medium remains out of reach for current observations. Detecting this emission would provide constraints on the nonthermal pressure support by CR protons in these environments. Aims: We provide estimates for diffuse $γ$-ray emission in the \textit{Fermi}-LAT band from galaxy clusters and the cosmic web in the local Universe. Methods: In this work, we show results from the first cosmological magnetohydrodynamic simulation with an on-the-fly spectral CR model. We modeled CR injection at shocks, accounted for adiabatic energy changes and advection of CR protons, and obtained their $γ$-ray emissivity directly from the simulated CR energy density and spectra. To do this, we used constrained initial conditions that evolved in a field closely resembling that of the local Universe, allowing a direct comparison to \textit{Fermi}-LAT data on massive clusters. Results: We find CR proton acceleration at all structure formation and accretion shocks in galaxy clusters and cosmic web filaments. These protons provide the basis for diffuse $γ$-ray emission in these regimes. The absolute value of the diffuse $γ$-ray emission in our simulation lies a few orders of magnitude below the current upper limits found by \textit{Fermi}-LAT. Under the assumption of our model, a sensitivity of $F_γ< 10^{-11} \: γ~ \text{s}^{-1}~\text{cm}^{-2}$ would be required for a detection of diffuse emission in Coma. This provides a lower limit for diffuse emission from CR protons accelerated at structure formation shocks.

astro-ph.HE↗

arXiv2026

Braginskii Viscosity in Cosmological Simulations of Galaxy Clusters: Implementation, Validation, and First Application

We present the implementation of an anisotropic viscosity solver within the magnetohydrodynamics (MHD) framework of the TreeSPH code OpenGadget3. The solver models anisotropic viscous transport along magnetic field lines following the Braginskii formulation and includes physically motivated limiters based on the mirror and firehose instability thresholds, which constrain the viscous stress in weakly collisional plasmas. To validate the implementation, we performed a suite of standard test problems -- including two variants of the sound wave test, circularly and linearly polarized Alfven waves, fast magnetosonic wave, and the Kelvin-Helmholtz instability -- both with and without the plasma-instability limiters. The results show excellent agreement with the AREPO implementation of a similar anisotropic viscosity model, confirming the accuracy and robustness of our method. Our formulation integrates seamlessly within the individual adaptive timestepping framework of OpenGadget3, avoiding the need for subcycling. This provides efficient and stable time integration while maintaining physical consistency. Finally, we applied the new solver to a cosmological zoom-in simulation of a galaxy cluster as a proof-of-concept application, demonstrating its capability to model anisotropic transport and plasma microphysics in realistic large-scale environments. Our implementation offers a versatile and computationally efficient tool for studying anisotropic viscosity in magnetized astrophysical systems.

astro-ph.IM↗

arXiv2026

Improving divergence cleaning in cosmological SPMHD simulations

We implement the constrained hyperbolic/parabolic divergence cleaning algorithm into the cosmological smoothed particle magnetohydrodynamics (SPMHD) code {\sc OpenGadget3}, modifying the governing equations so that the scheme can be applied consistently in an expanding cosmological framework. This ensures that divergence errors in the magnetic field are actively propagated away and damped, rather than advected with the flow and partially controlled by source terms as in the previously employed Powell eight-wave approach. We validate the implementation on a series of standard test problems -- the advection of an artificial divergence pulse, the Orszag--Tang vortex, the Brio--Wu shock tube, and a magnetised Zeldovich pancake -- which confirm that the scheme reduces divergence errors while preserving the correct physical evolution. We then apply the method to a fully cosmological simulation of a massive galaxy cluster with $M_\mathrm{200c} \approx 10^{15}~\mathrm{M}_{\odot}$, and compare directly to the Powell-only approach. The overall density structure of the cluster is largely unchanged by the choice of divergence cleaning, and the magnetic field geometry and strength in the cluster core remain similar. In the cluster outskirts ($r \approx 1$--$3~h^{-1}$~Mpc), however, the magnetic field is amplified by a factor of 5--10 compared to the Powell-only run, while the divergence error is reduced by 2--3 orders of magnitude throughout the cluster volume. Our results suggest that accurate divergence control is essential for capturing magnetic field amplification in the low-density, poorly resolved outskirts of galaxy clusters.

astro-ph.CO↗

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↗

arXiv2025

The GHOSDT Simulations: II. Missing H$_2$ in Simulations of a Self-Regulated Interstellar Medium

Observations in the Galaxy and nearby spirals have established that the HI-to-H$_2$ transition at solar metallicity occurs at gas weight of $P_{\rm DE}/k_B\approx 10^4 \ \rm K \ cm ^{-3}$, similar to solar neighbourhood conditions. Even so, state-of-the-art models of a self-regulated interstellar medium underproduce the molecular fraction ($R_{\rm mol} \equiv M_{{\rm H}_2}/M_{HI}$) at solar neighbourhood conditions by a factor of $\approx2-4$. We use the GHOSDT suite of simulations at a mass resolution range of $100-0.25\ M_{\odot}$ (effective spatial resolution range of $\sim 20-0.05\ \rm pc$) run for 500 Myr to show how this problem is affected by modeling choices such as the inclusion of photoionizing radiation, assumed supernova energy, numerical resolution, inclusion of magnetic fields, and including a model for sub-grid clumping. We find that $R_{\rm mol}$ is not converged even at a resolution of 1 $M_{\odot}$, with $R_{\rm mol}$ increasing by a factor of 2 when resolution is improved from 10 to $1\ M_{\odot}$. Models excluding either photoionization or magnetic fields result in a factor 2 reduction in $R_{\rm mol}$. The only model that agrees with the observed value of $R_{\rm mol}$ includes our sub-grid clumping model, which enhances $R_{\rm mol}$ by a factor of $\sim3$ compared with our fiducial model. This increases the time-averaged $R_{\rm mol}$ to $0.25$, in agreement with the Solar circle value, and closer to the observed median value of $0.42$ in regions comparable to the solar neighbourhood in nearby spirals. Our findings show that small-scale clumping in the ISM plays a significant role in H$_2$ formation even in high-resolution numerical simulations.

astro-ph.GA↗

arXiv2025

Much Ado About Nothing: Galaxy Formation and Galactic Outflows in Cosmic Voids

We present a theoretical framework for calculating the volume filling fraction of galactic outflows in cosmic voids by integrating analytical models for the halo mass function (HMF), the halo occupation fraction, the stellar mass-halo mass relation, and outflow sizes. Using RAMSES, we perform a hydrodynamical zoom-in simulation of the central 25 cMpc/h region of a spherical void, identified as the lowest-density region among 1,000 random spheres in a parent 1 Gpc box simulation. This void has a diameter of 120 cMpc/h and a density contrast of $δ\simeq -0.8$. We find that the properties of void galaxies remain stable when expanding the zoom-in region to 50 cMpc/h, though our relatively low mass resolution impacts the results. Our higher-resolution simulation aligns with the analytical HMF that accounts for the void's underdensity and size. While higher resolution improves stellar mass estimates for low-mass halos, computational constraints necessitate a theoretical framework that enables extrapolation to infinite resolution. Our analytical model, calibrated to our simulations, enables extrapolation down to the filtering mass of star-forming halos. To compare galaxy properties in this void with those in the field, we conduct a companion field simulation of the same box size. At infinite resolution, we predict wind volume filling fractions of $18.6\%$ in the field and $3.1\%$ in our void, with values dependent on cosmic variance, void size, and underdensity. Dwarf galaxies contribute minimally, and resolving halos to $M_{\rm h}=10^{10} M_\odot$ suffices for robust estimates. Applying our framework to the Local Group void ($δ\simeq -0.5$, $R=20\ \mathrm{cMpc}$), we predict a wind volume filling fraction of $9.6\%\pm3.3\%$.

astro-ph.GA↗

arXiv2025

Simulating the LOcal Web (SLOW) V. Thermodynamic Properties and Evolution of Local Galaxy Clusters

The intracluster medium (ICM), composed of hot plasma, dominates the baryonic content of galaxy clusters and is primarily observable in X-rays. Its thermodynamic properties, pressure, temperature, entropy, and electron density, offer crucial insight into the physical processes shaping clusters, from accretion and mergers to radiative cooling and feedback. We investigate the thermodynamic properties of galaxy clusters in the Simulating the LOcal Web (SLOW) constrained simulations, which reproduce the observed large-scale structure of the local Universe. We assess how well these simulations reproduce observed ICM profiles and explore the connection between cluster formation history and core classification. Three-dimensional thermodynamic profiles are extracted and compared to deprojected X-ray and Sunyaev - Zel'dovich (SZ) data for local clusters classified as solid cool-core (SCC), weakly cool-core (WCC), and non-cool-core (NCC) systems. We also examine the mass assembly history of the simulated counterparts to link their formation to present-day ICM properties. The simulations reproduce global thermodynamic profiles for clusters such as Perseus, Coma, A85, A119, A1644, A2029, A3158, and A3266. Moreover, they show that CC clusters typically assemble their mass earlier, while NCC systems grow through more extended, late-time merger-driven histories. WCC clusters show intermediate behavior, suggesting an evolutionary transition. Our results demonstrate that constrained simulations provide a powerful tool for linking cluster formation history to present-day ICM properties and point to possible refinements in subgrid physics as well as in resolution that could improve the agreement in cluster core regions.

astro-ph.CO↗

arXiv2025

ASURA-FDPS-ML: Star-by-star Galaxy Simulations Accelerated by Surrogate Modeling for Supernova Feedback

We introduce new high-resolution galaxy simulations accelerated by a surrogate model that reduces the computation cost by approximately 75 percent. Massive stars with a Zero Age Main Sequence mass of more than about 10 $\mathrm{M_\odot}$ explode as core-collapse supernovae (CCSNe), which play a critical role in galaxy formation. The energy released by CCSNe is essential for regulating star formation and driving feedback processes in the interstellar medium (ISM). However, the short integration timesteps required for SNe feedback have presented significant bottlenecks in astrophysical simulations across various scales. Overcoming this challenge is crucial for enabling star-by-star galaxy simulations, which aim to capture the dynamics of individual stars and the inhomogeneous shell's expansion within the turbulent ISM. To address this, our new framework combines direct numerical simulations and surrogate modeling, including machine learning and Gibbs sampling. The star formation history and the time evolution of outflow rates in the galaxy match those obtained from resolved direct numerical simulations. Our new approach achieves high-resolution fidelity while reducing computational costs, effectively bridging the physical scale gap and enabling multi-scale simulations.

astro-ph.GA↗

arXiv2025

Zooming In On The Multi-Phase Structure of Magnetically-Dominated Quasar Disks: Radiation From Torus to ISCO Across Accretion Rates

Recent radiation-thermochemical-magnetohydrodynamic simulations resolved formation of quasar accretion disks from cosmological scales down to ~300 gravitational radii $R_{g}$, arguing they were 'hyper-magnetized' (plasma $β\ll1$ supported by toroidal magnetic fields) and distinct from traditional $α$-disks. We extend these, refining to $\approx 3\,R_{g}$ around a $10^{7}\,{\rm M_{\odot}}$ BH with multi-channel radiation and thermochemistry, and exploring a factor of 1000 range of accretion rates ($\dot{m}\sim0.01-20$). At smaller scales, we see the disks maintain steady accretion, thermalize and self-ionize, and radiation pressure grows in importance, but large deviations from local thermodynamic equilibrium and single-phase equations of state are always present. Trans-Alfvenic and highly-supersonic turbulence persists in all cases, and leads to efficient vertical mixing, so radiation pressure saturates at levels comparable to fluctuating magnetic and turbulent pressures even for $\dot{m}\gg1$. The disks also become radiatively inefficient in the inner regions at high $\dot{m}$. The midplane magnetic field remains primarily toroidal at large radii, but at super-Eddington $\dot{m}$ we see occasional transitions to a poloidal-field dominated state associated with outflows and flares. Large-scale magnetocentrifugal and continuum radiation-pressure-driven outflows are weak at $\dot{m}<1$, but can be strong at $\dot{m}\gtrsim1$. In all cases there is a scattering photosphere above the disk extending to $\gtrsim 1000\,R_{g}$ at large $\dot{m}$, and the disk is thick and flared owing to magnetic support (with $H/R$ nearly independent of $\dot{m}$), so the outer disk is strongly illuminated by the inner disk and most of the inner disk continuum scatters or is reprocessed at larger scales, giving apparent emission region sizes as large as $\gtrsim 10^{16}\,{\rm cm}$.

astro-ph.GA↗

arXiv2025

Delayed and Displaced: The Impact of Binary Interactions on Core-collapse SN Feedback

Core-collapse supernova feedback models in hydrodynamical simulations typically assume that all stars evolve as single stars. However, the majority of massive stars are formed in binaries and multiple systems, where interactions with a companion can affect stars' subsequent evolution and kinematics. We assess the impact of binary interactions on the timing and spatial distribution of core-collapse supernovae, using `cogsworth` simulations to evolve binary star populations, and their subsequent galactic orbits, within state-of-the-art hydrodynamical zoom-in galaxy simulations. We show that binary interactions: (a) displace supernovae, with ~13% of all supernovae occurring more than 0.1 kpc from their parent cluster; and (b) produce delayed supernovae, such that ~25% of all supernovae occur after the final supernova from a single star population. Delays are largest for low-mass merger products, which can explode more than 200 Myr after a star formation event. We characterize our results as a function of: (1) initial binary population distributions, (2) binary physics parameters and evolutionary pathways, (3) birth cluster dissolution assumptions, and (4) galaxy models (which vary metallicity, star formation history, gravitational potential and simulation codes), and show that the overall timing and spatial distributions of supernovae are surprisingly insensitive to most of these variations. We provide metallicity-dependent analytic fits that can be substituted for single-star subgrid feedback prescriptions in hydrodynamical simulations, and discuss some of the possible implications for binary-driven feedback in galaxies, which may become particularly important at high redshift.

astro-ph.SR↗

arXiv2025

The GHOSDT Simulations (Galaxy Hydrodynamical Simulations with Supernova-Driven Turbulence) -- I. Magnetic Support in Gas Rich Disks

Galaxies at redshift $z\sim 1-2$ display high star formation rates (SFRs) with elevated cold gas fractions and column densities. Simulating a self-regulated ISM in a hydrodynamical, self-consistent context, has proven challenging due to strong outflows triggered by supernova (SN) feedback. At sufficiently high gas column densities, if magnetic fields or other mitigating measures are not implemented, these outflows can prevent a quasi-steady disk from forming for several 100 Myr. To this end, we present GHOSDT, a suite of magneto-hydrodynamical simulations that implement ISM physics at high resolution. We demonstrate that magnetic pressure is important in the dense ISM of gas-rich star-forming disks. We show that a relation between the magnetic field and gas surface density emerges naturally from our simulations. We argue that the magnetic field in the dense, star-forming gas, may be set by the SN-driven turbulent gas motions. When compared to pure hydrodynamical runs, we find that the inclusion of magnetic fields increases the cold gas fraction by up to 40\%, reduces the disc scale height by up to a factor of $\sim 2$, and reduces the star formation burstiness. In dense ($n>100\;\rm{cm}^{-3}$) gas, we find steady-state magnetic field strengths of 10--40 $μ$G, comparable to those observed in Galactic molecular clouds. Finally, we demonstrate that our simulation framework is consistent with the Ostriker et al. (2022) Pressure Regulated Feedback Modulated Theory of star formation and stellar feedback.

astro-ph.GA↗

arXiv2025

Learning the Universe: physically-motivated priors for dust attenuation curves

Understanding the impact of dust on the spectral energy distributions (SEDs) of galaxies is crucial for inferring their physical properties and for studying the nature of interstellar dust. We analyze dust attenuation curves for $\sim 6400$ galaxies ($M_{\star} \sim 10^9 - 10^{11.5}\,M_{\odot}$) at $z=0.07$ in the IllustrisTNG50 and TNG100 simulations. Using radiative transfer post-processing, we generate synthetic attenuation curves and fit them with a parametric model that captures known extinction and attenuation laws (e.g., Calzetti, MW, SMC, LMC) and more exotic forms. We present the distributions of the best-fitting parameters: UV slope ($c_1$), optical-to-NIR slope ($c_2$), FUV slope ($c_3$), 2175 Angstrom bump strength ($c_4$), and normalization ($A_{\rm V}$). Key correlations emerge between $A_{\rm V}$ and the star formation rate surface density $Σ_{\rm SFR}$, as well as the UV slope $c_1$. The UV and FUV slopes ($c_1, c_3$) and the bump strength and visual attenuation ($c_4, A_{\rm V}$) exhibit robust internal correlations. Using these insights from simulations, we provide a set of scaling relations that predict a galaxy's median (averaged over line of sight) dust attenuation curve based solely on its $Σ_{\rm SFR}$ and/or $A_{\rm V}$. These predictions agree well with observed attenuation curves from the GALEX-SDSS-WISE Legacy Catalog despite minor differences in bump strength. This study delivers the most comprehensive library of synthetic attenuation curves for local galaxies, providing a foundation for physically motivated priors in SED fitting and galaxy inference studies, such as those performed as part of the Learning the Universe Collaboration.

astro-ph.GA↗

arXiv2024

Turbulent Pressure Support in Galaxy Clusters -- Impact of the Hydrodynamical Solver

The amount of turbulent pressure in galaxy clusters is still debated, especially as for the impact of the dynamical state and the hydro-method used for simulations. We study the turbulent pressure fraction in the intra cluster medium of massive galaxy clusters. We aim to understand the impact of the hydrodynamical scheme, analysis method, and dynamical state on the final properties of galaxy clusters from cosmological simulations. We perform non-radiative simulations of a set of zoom-in regions of seven galaxy clusters with Meshless Finite Mass (MFM) and Smoothed Particle Hydrodynamics (SPH). We use three different analysis methods based on: $(i)$ the deviation from hydrostatic equilibrium, $(ii)$ the solenoidal velocity component obtained by a Helmholtz-Hodge decomposition, and $(iii)$ the small-scale velocity obtained through a multi-scale filtering approach. We split the sample of simulated clusters into active and relaxed clusters. Our simulations predict an increased turbulent pressure fraction for active compared to relaxed clusters. This is especially visible for the velocity-based methods. For these, we also find increased turbulence for the MFM simulations compared to SPH, consistent with findings from more idealized simulations. The predicted non-thermal pressure fraction varies between a few percent for relaxed clusters and $\approx13\%$ for active ones within the cluster center and increases towards the outskirts. No clear trend with redshift is visible. Our analysis quantitatively assesses the importance played by the hydrodynamical scheme and the analysis method to determine the non-thermal/turbulent pressure fraction. While our setup is relatively simple (non-radiative runs), our simulations show agreement with previous, more idealized simulations, and make a step further toward the understanding of turbulence.

astro-ph.CO↗

arXiv2024

Simulating the LOcal Web (SLOW) -- III: Synchrotron emission from the local cosmic web

Aims: Detecting diffuse synchrotron emission from the cosmic web is still a challenge for current radio telescopes. We aim to make predictions about the detectability of cosmic web filaments from simulations. Methods: We present the first cosmological magnetohydrodynamic simulation of a 500 $h^{-1} c$Mpc volume with an on-the-fly spectral cosmic ray (CR) model. This allows us to follow the evolution of populations of CR electrons and protons within every resolution element of the simulation. We modeled CR injection at shocks, while accounting for adiabatic changes to the CR population and high-energy-loss processes of electrons. The synchrotron emission was then calculated from the aged electron population, using the simulated magnetic field, as well as different models for the origin and amplification of magnetic fields. We used constrained initial conditions, which closely resemble the local Universe, and compared the results of the cosmological volume to a zoom-in simulation of the Coma cluster, to study the impact of resolution and turbulent reacceleration of CRs on the results. Results: We find a consistent injection of CRs at accretion shocks onto cosmic web filaments and galaxy clusters. This leads to diffuse emission from filaments of the order $S_ν\approx 0.1 \: μ$Jy beam$^{-1}$ for a potential LOFAR observation at 144~MHz, when assuming the most optimistic magnetic field model. The flux can be increased by up to two orders of magnitude for different choices of CR injection parameters. This can bring the flux within a factor of ten of the current limits for direct detection. We find a spectral index of the simulated synchrotron emission from filaments of $α\approx$ -1.0 -- -1.5 in the LOFAR band.

astro-ph.CO↗

arXiv2024

Cosmological and Astrophysical Parameter Inference from Stacked Galaxy Cluster Profiles Using CAMELS-zoomGZ

We present a study on the inference of cosmological and astrophysical parameters using stacked galaxy cluster profiles. Utilizing the CAMELS-zoomGZ simulations, we explore how various cluster properties--such as X-ray surface brightness, gas density, temperature, metallicity, and Compton-y profiles--can be used to predict parameters within the 28-dimensional parameter space of the IllustrisTNG model. Through neural networks, we achieve a high correlation coefficient of 0.97 or above for all cosmological parameters, including $Ω_{\rm m}$, $H_0$, and $σ_8$, and over 0.90 for the remaining astrophysical parameters, showcasing the effectiveness of these profiles for parameter inference. We investigate the impact of different radial cuts, with bins ranging from $0.1R_{200c}$ to $0.7R_{200c}$, to simulate current observational constraints. Additionally, we perform a noise sensitivity analysis, adding up to 40\% Gaussian noise (corresponding to signal-to-noise ratios as low as 2.5), revealing that key parameters such as $Ω_{\rm m}$, $H_0$, and the IMF slope remain robust even under extreme noise conditions. We also compare the performance of full radial profiles against integrated quantities, finding that profiles generally lead to more accurate parameter inferences. Our results demonstrate that stacked galaxy cluster profiles contain crucial information on both astrophysical processes within groups and clusters and the underlying cosmology of the universe. This underscores their significance for interpreting the complex data expected from next-generation surveys and reveals, for the first time, their potential as a powerful tool for parameter inference.

astro-ph.CO↗

arXiv2024

Density Fluctuations in the Intracluster Medium: An Attempt to Constrain Viscosity with Cosmological Simulations

The impact of viscosity in the Intracluster Medium (ICM) is still an open question in astrophysics. To address this problem, we have run a set of cosmological simulations of three galaxy clusters with a mass larger than $M_{\mathrm{Vir}} > 10^{15} $M$_{\odot}$ at $z=0$ using the SPMHD-code OpenGadget3. We aim to quantify the influence of viscosity and constrain its value in the ICM. Our results show significant morphological differences at small scales, temperature variations, and density fluctuations induced by viscosity. We observe a suppression of instabilities at small scales, resulting in a more filamentary structure and a larger amount of small structures due to the lack of mixing with the medium. The conversion of kinetic to internal energy leads to an increase of the virial temperature of the cluster of $\sim$5% - 10%, while the denser regions remain cold. The amplitude of density and velocity fluctuations are found to increase with viscosity. However, comparison with observational data indicates that the simulations, regardless of the viscosity, match the observed slope of the amplitude of density fluctuations, challenging the direct constraint of viscosity solely through density fluctuations. Furthermore, the ratio of density to velocity fluctuations remains close to 1 regardless of the amount of viscosity, in agreement with the theoretical expectations. Our results show for the first time in a cosmological simulation of a galaxy cluster the effect of viscosity in the ICM, a study that is currently missing in the literature.

astro-ph.CO↗

arXiv2024

Towards Implementation of the Pressure-Regulated, Feedback-Modulated Model of Star Formation in Cosmological Simulations: Methods and Application to TNG

Traditional star formation subgrid models implemented in cosmological galaxy formation simulations, such as that of Springel & Hernquist (2003, hereafter SH03), employ adjustable parameters to satisfy constraints measured in the local Universe. In recent years, however, theory and spatially-resolved simulations of the turbulent, multiphase, star-forming ISM have begun to produce new first-principles models, which when fully developed can replace traditional subgrid prescriptions. This approach has advantages of being physically motivated and predictive rather than empirically tuned, and allowing for varying environmental conditions rather than being tied to local Universe conditions. As a prototype of this new approach, by combining calibrations from the TIGRESS numerical framework with the Pressure-Regulated Feedback-Modulated (PRFM) theory, simple formulae can be obtained for both the gas depletion time and an effective equation of state. Considering galaxies in TNG50, we compare the "native" simulation outputs with post-processed predictions from PRFM. At TNG50 resolution, the total midplane pressure is nearly equal to the total ISM weight, indicating that galaxies in TNG50 are close to satisfying vertical equilibrium. The measured gas scale height is also close to theoretical equilibrium predictions. The slopes of the effective equations of states are similar, but with effective velocity dispersion normalization from SH03 slightly larger than that from current TIGRESS simulations. Because of this and the decrease in PRFM feedback yield at high pressure, the PRFM model predicts shorter gas depletion times than the SH03 model at high densities and redshift. Our results represent a first step towards implementing new, numerically calibrated subgrid algorithms in cosmological galaxy formation simulations.

astro-ph.GA↗