arXiv subjects

Stefano Borgani

Publications and source records attributed to Stefano Borgani.

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

Dianoga simulations of galaxy clusters and groups: Properties of the baryonic components

We introduce the Dianoga set of cosmological simulations of galaxy clusters and groups, specifically aimed at studying the impact of the implementation of AGN feedback and star formation. Using the OpenGadget3 code, we carry out simulations of 28 regions centred on massive galaxy clusters, and of a cosmological box. This generates a sample of 293 halos with M_{200}> 1.5 x 10^{13} M_{\odot}. Parameters of AGN feedback in the reference implementation were minimally calibrated exclusively to match the local relation between SMBH masses and stellar masses of host galaxies. Simulations are compared to observed galaxy stellar mass function (GSMF), stellar mass fraction in clusters and groups, BCG masses, scaling relations between ICM/IGM properties and profiles of their thermodynamical properties. In the appendix, we show how results vary as we modify the reference feedback model in six alternative configurations. Our reference model predicts a GSMF in general agreement with observations, albeit overestimated in the high end. BCG stellar masses and mass fractions are higher than observed in massive clusters, while being closer to observations for groups. Predicted properties of the ICM/IGM are in general agreement with observations, with the core regions of simulated clusters having entropy and temperature profiles that are slightly less "cool-cored" than observed. A comparison with other implementations of AGN feedback highlights that models including thermal evaporation of the sub-resolution interstellar medium succeed to bring BCG masses and stellar mass fractions closer to observation, and to increase the cool-coreness of simulated clusters. Our results demonstrate that the details of the interface between AGN energy injection and the sub-resolution interstellar medium model are at least as critical as the total feedback efficiency itself.

astro-ph.CO↗

arXiv2026

Variability in Cosmological Hydrodynamical Simulations: how Stochastic Processes, Numerical Effects, and Reproducibility Limits impact Predictability

Cosmological hydrodynamical simulations are powerful tools for studying galaxy formation, yet their predictive precision is limited by stochastic variability and numerical uncertainty. We quantify this variability using four identical realizations of a zoom-in galaxy-cluster simulation evolved with \textsc{OpenGadget3} under tightly controlled compiler, library, and hardware settings. Variability is measured through the properties of matched galaxies across repeated runs, including a mixed linear model that separates run-to-run variation from within-run noise. Variations of approximately $10$-$25\%$ are found in galaxy dark matter and stellar masses for the baseline simulations. The variability trending above the shot-noise floor reflects the combined effects of stochastic star formation and feedback regulation, and is further amplified when black hole physics is included. Furthermore, our results indicate that feedback acts to regulate variability, reducing scatter in both stellar and black hole masses. Our inference from run-to-run variation indicates a noise-dominated regime that remains statistically reproducible, despite individual realization differences. These results establish baseline, noise-dominated variability estimates at low resolution, demonstrate how feedback modulates predictability, and provide a statistical framework for future studies of reproducibility in cosmological hydrodynamical simulations.

astro-ph.GA↗

arXiv2026

On the impact of baryons on the halo mass function, bias, and cluster cosmology

Luminous matter produces very energetic events, such as active galactic nuclei and supernova explosions, that significantly affect the internal regions of galaxy clusters. Although the current uncertainty in the effect of baryonic physics on cluster statistics is subdominant as compared to other systematics, the picture is likely to change soon as the amount of high-quality data is growing fast, urging the community to keep theoretical systematic uncertainties below the ever-growing statistical precision. In this paper, we study the effect of baryons on galaxy clusters, and their impact on the cosmological applications of clusters, using the Magneticum suite of cosmological hydrodynamical simulations. We show that the impact of baryons on the halo mass function can be recast in terms on a variation of the mass of the halos simulated with pure N-body, when baryonic effects are included. The halo mass function and halo bias are only indirectly affected. Finally, we demonstrate that neglecting baryonic effects on halos mass function and bias would significantly alter the inference of cosmological parameters from high-sensitivity next-generations surveys of galaxy clusters.

astro-ph.CO↗

arXiv2026

Accurate cosmological emulator for the probability distribution function of gravitational lensing of point sources

We develop an accurate and computationally efficient emulator to model the gravitational lensing magnification probability distribution function (PDF), enabling robust cosmological inference of point sources such as supernovae and gravitational-wave observations. We construct a pipeline utilizing cosmological $N$-body simulations, creating past light cones to compute convergence and shear maps. Principal Component Analysis (PCA) is employed for dimensionality reduction, followed by an eXtreme Gradient Boosting (XGBoost) machine learning model to interpolate magnification PDFs across a broad cosmological parameter space ($Ω_m$, $σ_8$, $w$, $h$) and redshift range ($0.2 \le z \le 6$). We identify the optimal number of PCA components to balance accuracy and stability. Our emulator, publicly released as ace_lensing, accurately reproduces lensing PDFs with a median Kullback-Leibler divergence of $0.007$. Validation on the test set confirmed that the model reliably reproduces the detailed shapes and statistical properties of the PDFs across the explored parameter range, showing no significant degradation for specific parameter combinations or redshifts. Future work will focus on incorporating baryonic physics through hydrodynamical simulations and expanding the training set to further enhance model accuracy and generalizability.

astro-ph.CO↗

arXiv2025

X-ray view of a massive node of the Cosmic Web at z=3 II. Discovery of extended X-ray emission around a hyperluminous QSO

While the warm, ionized gas in the CGM at z>3 is now routinely observed around bright QSOs in Lya emission, little is known about the CGM hot phase due to its expected faintness in the X-ray band, often referred to as the ICM. Here, we report the analysis of 634 ks of Chandra X-ray observations in the MQN01 Cosmic Node, a region containing one of the brightest Lya nebulae and the largest galaxy overdensity discovered so far at z>3. We detect 66 net counts of X-ray emission in the 0.5-2 keV band extending to at least 30 kpc from the brightest QSO in MQN01. The morphology and spectrum are consistent with thermal emission from hot plasma in CIE. Photoionization is negligible, and IC is disfavored. A joint spatial and spectral MCMC analysis provides consistency with a beta-model with a steep density profile and a gas temperature kT~1.8 keV and virial halo mass Mvir~3e13 Mo. The inferred hot gas mass is Mhot(<Rvir)~2.6e12 Mo, which is ~8.3% of Mvir, or ~56% of the theoretical cosmological baryon budget of the halo. The hot gas also emits an exceptionally high Lx, with a measured L2-10~2.3e45 erg/s within the central 30 kpc. This system is a clear outlier in the Lx-Tx plane, indicating a thermodynamic state distinct from that of evolved lower-redshift hot halos. The cooling time in the inner 15-30 kpc is comparable to the local dynamical time, suggesting that the gas could become locally unstable in the absence of heating or feedback. Moreover, the thermal pressure associated with the detected CGM hot phase is large enough to confine the cold and dense clumps, which are required to reproduce the high Lya emission associated with the inner regions of the MQN01 structure. Although limited to a single system, our results provide unique information on the multi-phase properties of the CGM and a view of the nascent thermal hot gas phase observed in local galaxy clusters.

astro-ph.GA↗

arXiv2025

DUCA: Dynamic Universe Cosmological Analysis. II. The impact of clustering dark energy on the halo mass function

Galaxy clusters are powerful probes of cosmology, and the halo mass function (HMF) serves as a fundamental tool for extracting cosmological information. Previous calibrations of the HMF in dynamical dark energy (DE) models either assumed a homogeneous DE component or a fixed sound speed of unity, which strongly suppresses DE perturbations. We extend the HMF calibration to clustering dark energy (CDE) models by allowing for a sound speed $(c_{\rm s})$ value different than unity. This generalization enables a broader description of the impact of DE perturbations on structure formation. Our approach builds upon the DUCA simulation suite that accounts for DE at the background and perturbative levels. We present an HMF calibration based on introducing an effective peak height while maintaining the multiplicity function as previously calibrated. The effective peak height is written as a function of the peak height computed using the matter power spectrum of the homogeneous DE case, but it is modulated by the amplitude of DE and matter perturbations on the non-homogeneous case at the turnaround. The model depends on one single parameter, which we calibrate using $N$-body simulations, following a Bayesian approach. The resulting HMF model achieves sub-percent accuracy over a wide range of $c_{\rm s}$ values. Our analysis reveals that, although the overall impact of CDE on halo abundances remains modest (typically a few percent), the effects are more pronounced in non-phantom DE scenarios. Our model qualitatively agrees with predictions based on the spherical collapse model, but predicts a significantly lower impact for low $c_{\rm s}$. Our results underscore the need for more precise modeling of CDE's nonlinear regime. Numerical simulations and theoretical approaches must be advanced to capture the complex interplay between DE perturbations and matter fully.

astro-ph.CO↗

arXiv2025

Dynamical friction and massive black hole orbits: analytical predictions and numerical solutions

We investigate the orbital decay of a massive BH embedded in a dark matter halo and a stellar bulge, using both analytical and numerical simulations with the aim of developing and validating a reliable dynamical friction (DF) correction across simulation resolutions. We develop a Python-based library to solve the equations of motion of the BH and provide an analytical framework for the numerical results. Then, we carry out simulations at different resolutions and for different softening choices using the Tree-PM code OpenGADGET3, where we implement an improved DF correction based on a kernel-weighted local density estimation. Our results demonstrate that the DF correction significantly accelerates BH sinking and ensures convergence with increasing resolution, closely matching analytical predictions. We find that in low-resolution regimes - particularly when the BH mass is smaller than that of the background particles - our DF model still effectively controls BH dynamics. Contrary to expectations, the inclusion of a stellar bulge can delay sinking due to numerical heating, an effect partially mitigated by the DF correction. We conclude that our refined DF implementation provides a robust framework for modeling BH dynamics both in controlled simulation setups of galaxies and in large-scale cosmological simulations. This will be crucial for future simulation campaigns, to enable more accurate predictions of AGN accretion and feedback, and to estimate gravitational-wave event rates.

astro-ph.GA↗

arXiv2025

The Three Hundred Project: Modeling Baryon and Hot-Gas Fraction Evolution in Simulated Clusters

The baryon fraction of galaxy clusters is a powerful tool to inform on the cosmological parameters while the hot-gas fraction provides indications on the physics of the intracluster plasma and its interplay with the processes driving galaxy formation. Using cosmological hydrodynamical simulations from The Three Hundred collaboration of about 300 simulated massive galaxy clusters with median mass $M_{500}\approx7 \times 10^{14}$M$_{\odot}$ at $z=0$, we model the relations between total mass and either baryon fraction or the hot gas fractions at overdensities $Δ= 2500$, $500$, and $200$ with respect to the cosmic critical density, and their evolution from $z\sim 0$ to $z\sim 1.3$. We fit the simulation results for such scaling relations against three analytic forms (linear, quadratic, and logarithmic in a logarithmic plane) and three forms for the redshift dependence, considering as a variable both the inverse of cosmic scale factor, $(1+z)$, and the Hubble expansion rate, $E(z)$. We show that power-law dependencies on cluster mass poorly describe the investigated relations. A power-law fails to simultaneously capture the flattening of the total baryon and gas fractions at high masses, their drop at the low masses, and the transition between these two regimes. The other two functional forms provide a more accurate description of the curvature in mass scaling. The fractions measured within smaller radii exhibit a stronger evolution than those measured within larger radii. From the analysis of these simulations, we conclude that as long as we include systems in the mass range herein investigated, the baryon or gas fraction can be accurately related to the total mass through either a parabola or a logarithm in the logarithmic plane. The trends are common to all modern hydro simulations, although the amplitude of the drop at low masses might differ [Abridged].

astro-ph.CO↗

arXiv2025

The full iron budget in simulated galaxy clusters: The chemistry between gas and stars

Heavy chemical elements such as iron in the intra-cluster medium (ICM) of galaxy clusters are a signpost of the interaction between the gas and stellar components. Observations of the ICM metallicity in present-day massive systems, however, pose a challenge to the underlying assumption that the cluster galaxies have produced the amount of iron that enriches the ICM. We evaluate the iron share between ICM and stars within simulated galaxy clusters with the twofold aim of investigating the origin of possible differences with respect to observational findings and of shedding light on the observed excess of iron on the ICM with respect to expectations based on the observed stellar population. We evaluated the iron mass in gas and stars in a sample of 448 simulated systems with masses M500 > 1e14 Msun at z=0.07. These were extracted from the high-resolution (352 cMpc/h)^3 volume of the Magneticum cosmological hydrodynamical simulations. We compared our results with observational data of low-redshift galaxy clusters. The iron share in simulated clusters features a shallow dependence on the total mass, and its value is close to unity on average. In the most massive simulated systems, the iron share is thus smaller than observational values by almost an order of magnitude. The dominant contribution to this difference is related to the stellar component, whereas the chemical properties of the ICM agree well overall with the observations. We find larger stellar mass fractions in simulated massive clusters, which in turn yield higher stellar iron masses, than in observational data. Consistently with the modelling, we confirm that the stellar content within simulated present-day massive systems causes the metal enrichment in the ICM. It will be crucial to alleviate the stellar mass discrepancy between simulations and observations to definitely assess the iron budget in galaxy clusters.

astro-ph.CO↗

arXiv2025

DUCA: Dynamic Universe Cosmological Analysis. I. The halo mass function in dynamical dark energy cosmologies

The halo mass function (HMF) is fundamental for interpreting the number counts of galaxy clusters, serving as a pivotal theoretical tool in cosmology. With the advent of high-precision surveys such as LSST, eROSITA, DESI, and Euclid, accurate HMF modeling becomes indispensable to avoid systematic biases in cosmological parameter estimation from cluster cosmology. Moreover, these surveys aim to shed light on the dark sector and uncover dark energy's puzzling nature, necessitating models that faithfully capture its features to ensure robust parameter inference. We aim to construct a model for the HMF in dynamical dark energy cosmologies that preserves the accuracy achieved for the standard $Λ(ν)$CDM model of cosmology, while meeting the precision requirements necessary for future cosmological surveys. Our approach models the HMF parameters as functions of the deceleration parameter at the turnaround, a quantity shown to encapsulate essential information regarding the impact of dynamical dark energy on structure formation. We calibrate the model using results from a comprehensive suite of $N$-body simulations spanning various cosmological scenarios, ensuring sub-percent systematic accuracy. We present an HMF model tailored for dynamical dark energy cosmologies. The model is calibrated following a Bayesian approach, and its uncertainty is characterized by a single parameter controlling its systematic error, which remains at the sub-percent level. This ensures that theoretical uncertainties from our model are subdominant relative to other error sources in future cluster number counts analyses.

astro-ph.CO↗

arXiv2025

Numerical limits in the integration of Vlasov-Poisson equation for Cold Dark Matter

The Vlasov-Poisson systems of equations (VP) describes the evolution of a distribution of collisionless particles under the effect of a collective-field potential. VP is at the basis of the study of the gravitational instability of cosmological density perturbations in Dark-Matter (DM), but its range of application extends to other fields, such as plasma physics. In the case of Cold Dark Matter, a single velocity is associated with each fluid-element (or particle) , the initial condition presents a stiff discontinuity. This creates problems such as diffusion or negative distribution function when a grid based method is used to solve VP. In this work we want to highlight this problem, focusing on the technical aspects of this phenomenon. By comparing different finite volume methods and a spectral method we observe that, while all integration schemes preserve the invariants of the system (e.g, energy), the physical observable of interest, i.e., the density, is not correctly reproduced. We thus compare the density obtained with the different Eulerian integration schemes with the result obtained from a reference N-body method. We point out that the most suitable method to solve the VP system for a self-gravitating system is a spectral method.

physics.comp-ph↗

arXiv2025

The Three Hundred Project hydrodynamical simulations: Hydrodynamical weak-lensing cluster mass biases and richnesses using different hydro models

The mass of galaxy clusters estimated from weak-lensing observations is affected by projection effects, leading to a systematic underestimation compared to the true cluster mass, varying with both mass and redshift. The magnitude depends on the criteria used to select clusters and the spatial scale over which their mass is measured. We leverage hydrodynamical simulations of galaxy clusters carried out with GadgetX and GIZMO-SIMBA as part of the Three Hundred project. We used them to quantify weak-lensing mass biases with respect also to the results from dark matter-only simulations. We also investigate how the biases propagate into the richness-mass relation. We aim to shed light on the effect of the presence of baryons on the weak-lensing mass bias and also whether this bias depends on the galaxy formation recipe; we seek to model the richness-mass relation that can be used as guidelines for observational experiments for cluster cosmology. We produced weak-lensing simulations of random projections to model the expected excess surface mass density profile of clusters up to redshift $z=1$. We then estimated the observed richness by counting the number of galaxies in a cylinder and correcting by projected contaminants. We derived the weak-lensing mass-richness relation and found consistency across hydrodynamical simulations. The intercept parameter of the relation is independent of redshift but varies with the minimum of the stellar mass to define the richness. At the same time, the slope is relatively constant up to $z=0.55$. The scatter in observed richness at a fixed weak-lensing mass increases linearly with redshift at a fixed stellar mass cut. As expected, we observed that the scatter in richness at a given true mass is smaller than at a given weak-lensing mass. Our results for the weak-lensing mass-richness relation align well with SDSS redMaPPer cluster analyses. [Abridged]

astro-ph.CO↗

arXiv2025

On the Robustness of Cluster Clustering Covariance Calibration

Ongoing and upcoming wide-field surveys at different wavelengths will measure the distribution of galaxy clusters with unprecedented precision, demanding accurate models for the two-point correlation function (2PCF) covariance. In this work, we assess a semi-analytical framework for the cluster 2PCF covariance that employs three nuisance parameters to account for non-Poissonian shot noise, residual uncertainties in the halo bias model, and subleading noise terms. We calibrate these parameters on a suite of fast approximate simulations generated by PINOCCHIO as well as full $N$-body simulations from OpenGADGET3. We demonstrate that PINOCCHIO can reproduce the 2PCF covariance measured in OpenGADGET3 at the few percent level, provided the mass functions are carefully rescaled. Resolution tests confirm that high particle counts are necessary to capture shot-noise corrections, especially at high redshifts. We perform the parameter calibration across multiple cosmological models, showing that one of the nuisance parameters, the non-Poissonian shot-noise correction $α$, depends mildly on the amplitude of matter fluctuations $σ_8$. In contrast, the remaining two parameters, $β$ controlling the bias correction and $γ$ controlling the secondary shot-noise correction, exhibit more significant variation with redshift and halo mass. Overall, our results underscore the importance of calibrating covariance models on realistic mock catalogs that replicate the selection function of forthcoming surveys and highlight that approximate methods, when properly tuned, can effectively complement full $N$-body simulations for precision cluster cosmology.

astro-ph.CO↗

arXiv2025

Galaxy populations of ProtoClusters in cosmological hydrodynamical simulations

The study of protoclusters at cosmic noon is essential to understand the impact on galaxies of the environment and of the transformational processes occurring in this epoch. This work tests the predictions of the DIANOGA cosmological hydrodynamical simulations of cluster progenitors at z=2.2, comparing them with observations, and investigates the environmental effects on galaxies by comparing protoclusters with an average volume of the Universe. We analyze 14 protoclusters and a cosmological box of 49 cMpc/h per side. We compare predictions and observations of the galaxy properties, including colors of galaxies obtained with radiative transfer, to analyze UVJ diagrams. We showed that the DIANOGA simulations produce a galaxy stellar mass function in broad agreement with observations, with a higher fraction of high-mass galaxies ($M_{\ast}>10^{10} \ M_{\odot}$) in massive halos in protoclusters, compared to the box. The same signal, with lower significance, is also observed in the wide-field protocluster structures, indicating an accelerated evolution of galaxies before their infall into massive halos. Our simulations underestimate SFRs of galaxies both in protoclusters and in the box, compared to observations, due to low gas reservoirs. We find a weak suppression of SFRs in protocluster galaxies (~0.05 dex), compared to the box, increasing up to ~0.25 dex in massive halos. The quenched galaxy fraction varies significantly across different protocluster halos, consistent with observations. The simulations show a strong dependence of quenched fractions on halo mass and an excess of quenched galaxies in the wide-field protocluster region, compared to the cosmological box. UVJ diagram analysis shows qualitative agreement with observed color distributions of star-forming and quenched galaxies, except for few massive galaxies with steeper reddening vectors than typically assumed in observations.

astro-ph.GA↗

arXiv2024

Dynamical friction and evolution of black holes in cosmological simulations: a new implementation in OpenGadget3

We implement a sub-resolution prescription for the unresolved dynamical friction onto black holes (BHs) in the OpenGadget3 code. We carry out cosmological simulations of a volume of 16 cMpc3 and zoom-ins of a galaxy group and of a galaxy cluster. The advantages of our new technique are assessed in comparison to commonly adopted methods to hamper spurious BH displacements, i.e. repositioning onto a local minimum of the gravitational potential and ad-hoc boosting of the BH particle dynamical mass. The newly-introduced dynamical friction correction provides centering of BHs on host halos which is at least comparable with the other techniques. It predicts half as many merger events with respect to the repositioning prescription, with the advantage of being less prone to leave sub-structures without any central BH. Simulations featuring our dynamical friction prescription produce a smaller (by up to 50% with respect to repositioning) population of wandering BHs and final BH masses in good agreement with observations. As for individual BH-BH interactions, our dynamical friction model captures the gradual inspiraling of orbits before the merger occurs. By contrast, the repositioning scheme, in its most classical renditions considered, describes extremely fast mergers, while the dynamical mass misrepresents the BHs' dynamics, introducing numerical scattering between the orbiting BHs. Given its performances in describing the centering of BHs within host galaxies and the orbiting of BH pair before their merging, our dynamical friction correction opens interesting applications for an accurate description of the evolution of BH demography within cosmological simulations of galaxy formation at different cosmic epochs and within different environments.

astro-ph.CO↗

arXiv2024

Intertwined Formation of $\rm{H_2}$, Dust, and Stars in Cosmological Simulations

Context: Molecular hydrogen ($\rm{H_2}$) is crucial in galaxy formation and evolution, serving as the main fuel for star formation (SF). In metal-enriched environments, $\rm{H_2}$ primarily forms on interstellar dust grain surfaces. However, due to the complexities of modelling this process, SF in cosmological simulations often relies on empirical or theoretical frameworks validated only in the Local Universe to estimate the abundance of $\rm{H_2}$. Aims: This study aims to model the connection between star, dust, and $\rm{H_2}$ formation processes in cosmological simulations. Methods: We include $\rm{H_2}$ formation on dust grain surfaces and account for molecule destruction and radiation shielding into the SF and feedback model MUPPI. Results: The model reproduces key properties of observed galaxies for stellar, dust, and $\rm{H_2}$ components. The cosmic density of $\rm{H_2}$ ($ρ_{\rm{H2}}$) peaks around $z=1.5$, then decreases by half towards $z=0$, showing milder evolution than observed. The $\rm{H_2}$ mass function since $z=2$ also shows gentler evolution. Our model successfully recovers the integrated molecular Kennicutt-Schmidt (mKS) law between surface star formation rate ($Σ_{\rm SFR}$) and surface $\rm{H_2}$ density ($Σ_{\rm H2}$) at $z=0$, already evident at $z=2$ with a higher normalization. We find hints of a broken power law with a steeper slope at higher $Σ_{\rm H2}$, aligning with some observational findings. Additionally, the $\rm{H_2}$-to-dust mass ratio in galaxies shows a decreasing trend with gas metallicity and stellar mass. The $\rm{H_2}$-to-dust mass fraction for the global galaxy population is higher at higher redshifts. The analysis of the atomic-to-molecular transition on a particle-by-particle basis suggests that gas metallicity cannot reliably substitute the dust-to-gas ratio in models simulating dust-promoted $\rm{H_2}$.

astro-ph.GA↗

arXiv2024

Properties of the diffuse gas component in filaments detected in the Dianoga cosmological simulations

Hydrodynamical cosmological simulations are ideal laboratories where the evolution of the cosmic web can be studied. This allows for easier insight into the nature of the filaments. We investigate how the intrinsic properties of filaments are evolving in areas extracted from a larger cosmological simulation. We aim to identify significant trends in the properties of Warm-Hot Intergalactic Medium (WHIM) and suggest possible explanations. To study the filaments and their contents, we select a subset of regions from the Dianoga simulation. We analysed these regions that were simulated with different baryon physics, namely with and without the AGN feedback. We construct the cosmic web using the Sub-space Constrained Mean Shift (SCMS) algorithm and the Sequential Chain Algorithm for Resolving Filaments (SCARF). We examined the basic physical properties of filaments (length, shape, mass, radius) and analysed different gas phases (hot, WHIM and colder gas components) within those structures. The evolution of the global filament properties and the properties of the gas phases were studied in the redshift range $0 < z < 1.48$. Within our simulations, the detected filaments have, on average, lengths below $9$ Mpc. The filaments' shape correlates with their length; the longer they are, the more likely they are curved. We find that the scaling relation between mass $M$ and length $L$ of the filaments is well described by the power law $M \propto L^{1.7}$. The radial density profile is widening with redshift, meaning that the radius of the filaments is getting larger over time. The fraction of gas mass in the WHIM phase does not depend on the model and is rising towards lower redshifts. However, the included baryon physics has a strong impact on the metallicity of gas in filaments, indicating that the AGN feedback impacts the metal content already at redshifts of $z \sim 2$.

astro-ph.CO↗