Massive Galaxy Clusters Research Articles

Identification of High-redshift Galaxy Overdensities in GOODS-N and GOODS-S

We conduct a systematic search for high-redshift galaxy overdensities at 4.9 < z spec < 8.9 in both the Great Observatories Origins Deep Survey (GOODS)-N and GOODS-S fields using James Webb Space Telescope/Near-Infrared Camera (JWST/NIRCam) imaging from the JWST Advanced Deep Extragalactic Survey and JWST Extragalactic Medium-band Survey in addition to JWST/NIRCam wide field slitless spectroscopy from the First Reionization Epoch Spectroscopic Complete Survey. High-redshift galaxy candidates are identified using Hubble Space Telescope + JWST photometry spanning λ = 0.4–5.0 μm. We confirmed the redshifts for roughly a third of these galaxies using JWST spectroscopy over λ = 3.9–5.0 μm through identification of either Hα or OIIIλ5008 around the best-fit photometric redshift. The rest-ultraviolet magnitudes and continuum slopes of these galaxies were inferred from the photometry: the brightest and reddest objects appear in more dense environments and thus are surrounded by more galaxy neighbors than their fainter and bluer counterparts, suggesting accelerated galaxy evolution within overdense environments. We find 17 significant (δ gal ≥ 3.04, N gal ≥ 4) galaxy overdensities across both fields (seven in GOODS-N and 10 in GOODS-S), including the two highest redshift spectroscopically confirmed galaxy overdensities to date at zspec=7.954 and zspec=8.222 (representing densities around ∼6 and ∼12 times that of a random volume). We estimate the total halo mass of these large-scale structures to be 11.5≤log10Mhalo/M⊙≤13.4 using an empirical stellar mass-to-halo mass relation, which are likely underestimates as a result of incompleteness. These protocluster candidates are expected to evolve into massive galaxy clusters with log10Mhalo/M⊙≳14 by z = 0.

The Three Hundred: The existence of massive dark matter-deficient satellite galaxies in cosmological simulations

The observation of a massive galaxy with an extremely low dark matter content (i.e. NGC 1277) has posed questions about how such objects form and evolve in a hierarchical universe. We here report on the finding of several massive, dark matter-deficient galaxies in a set of 324 galaxy clusters theoretically modelled by means of full-physics hydrodynamical simulations. We first focus on two example galaxies selected amongst the most massive and dark matter-deficient ones. By tracing the evolution of these galaxies, we find that their lack of dark matter is a result of multiple pericentre passages. While orbiting their host halo, tidal interactions gradually strip away dark matter while preserving the stellar component. A statistical analysis of all massive satellite galaxies in the simulated clusters shows that the stellar-to-total mass ratio today is strongly influenced by the number of orbits and the distance at pericentres. Galaxies with more orbits and closer pericentres are more dark matter-deficient. Additionally, we find that massive, dark matter-deficient galaxies at the present day are either the remnants of very massive galaxies at infall or former central galaxies of infalling groups. We conclude that such massive yet dark matter-deficient galaxies exist and are natural by-products of typical cluster galaxy evolution, with no specific requirement for an exotic formation scenario.

NOEMA formIng Cluster survEy (NICE): Characterizing eight massive galaxy groups at 1.5 &lt; z &lt; 4 in the COSMOS field

The NOrthern Extended Millimeter Array (NOEMA) formIng Cluster survEy (NICE) is a NOEMA large programme targeting 69 massive galaxy group candidates at z &gt; 2 over six deep fields with a total area of 46 deg2. Here we report the spectroscopic confirmation of eight massive galaxy groups at redshifts 1.65 ≤ z ≤ 3.61 in the Cosmic Evolution Survey (COSMOS) field. Homogeneously selected as significant overdensities of red IRAC sources that have red Herschel colours, four groups in this sample are confirmed by CO and [CI] line detections of multiple sources with NOEMA 3 mm observations, three are confirmed with Atacama Large Millimeter Array (ALMA) observations, and one is confirmed by Hα emission from Subaru/FMOS spectroscopy. Using rich ancillary data in the far-infrared and sub-millimetre, we constructed the integrated far-infrared spectral energy distributions for the eight groups, obtaining a total infrared star formation rate (SFR) of 260–1300 M⊙ yr−1. We adopted six methods for estimating the dark matter masses of the eight groups, including stellar mass to halo mass relations, overdensity with galaxy bias, and NFW profile fitting to radial stellar mass densities. We find that the radial stellar mass densities of the eight groups are consistent with a NFW profile, supporting the idea that they are collapsed structures hosted by a single dark matter halo. The best halo mass estimates are log(Mh/M⊙) = 12.8 − 13.7 with a general uncertainty of 0.3 dex. Based on the halo mass estimates, we derived baryonic accretion rates (BARs) of (1 − 8)×103 M⊙/yr for this sample. Together with massive groups in the literature, we find a quasi-linear correlation between the integrated SFR/BAR ratio and the theoretical halo mass limit for cold streams, Mstream/Mh, with SFR/BAR = 10−0.46 ± 0.22(Mstream/Mh)0.71 ± 0.16 with a scatter of 0.40 dex. Furthermore, we compared the halo masses and the stellar masses with simulations, and find that the halo masses of all structures are consistent with those of progenitors of Mh(z = 0) &gt; 1014 M⊙ galaxy clusters, and that the most massive central galaxies have stellar masses consistent with those of the brightest cluster galaxy progenitors in the TNG300 simulation. Above all, the results strongly suggest that these massive structures are in the process of forming massive galaxy clusters via baryonic and dark matter accretion.

Inferring the Mass Content of Galaxy Clusters with Satellite Kinematics and Jeans Anisotropic Modeling

Satellite galaxies can be used to indicate the dynamic mass of galaxy groups and clusters. In this study, we apply the axisymmetric Jeans Anisotropic Multi-Gaussian Expansion (JAM) modeling to satellite galaxies in 28 galaxy clusters selected from the TNG300-1 simulation with halo masses of log10M200/M⊙>14.3 . If using true bound satellites as tracers, the best constrained total mass within the half-mass radius of satellites, M(<r half), and the virial mass, M 200, have average biases of −0.01 and 0.03 dex, with average scatters of 0.11 dex and 0.15 dex. If selecting companions in the redshift space with a line-of-sight depth of 2000 km s−1, the biases are −0.06 and 0.01 dex, while the scatters are 0.12 and 0.18 dex for M(<r half) and M 200. By comparing the best-fitting and actual density profiles, we find that ∼29% of the best-fitting density profiles show very good agreement with the truth, ∼32% display over/underestimates at most of the radial range with biased M(<r half), and 39% show under/overestimates in central regions and over/underestimates in the outskirts, with good constraints on M(<r half); yet most of the best constraints are still consistent with the true profiles within 1σ statistical uncertainties for the three circumstances. Using a mock DESI Bright Galaxy Survey catalog with the effect of fiber incompleteness, we find DESI fiber assignments and the choice of flux limits barely modify the velocity dispersion profiles and are thus unlikely to affect the dynamical modeling outcomes. Our results show that with current and future deep spectroscopic surveys, JAM can be a powerful tool to constrain the underlying density profiles of individual massive galaxy clusters.

Inferring galaxy cluster masses from cosmic microwave background lensing with neural simulation based inference

Gravitational lensing by massive galaxy clusters distorts the observed cosmic microwave background (CMB) on arcminute scales, and these distortions carry information about cluster masses. Standard approaches to extracting cluster mass constraints from the CMB cluster lensing signal are either sub-optimal, ignore important physical or observational effects, are computationally intractable, or require additional work to turn the lensing measurements into constraints on cluster masses. We apply simulation based inference (SBI) using neural likelihood models to the problem. We show that in circumstances where the exact likelihood can be computed, the SBI constraints on cluster masses are in agreement with the exact likelihood, demonstrating that the SBI constraints are close to optimal. In scenarios where the exact likelihood cannot be feasibly computed, SBI still recovers unbiased estimates of individual cluster masses and combined constraints from multiple clusters. SBI will be a powerful tool for constraining the masses of galaxy clusters detected by future cosmic surveys. Code to run the analyses presented here will be made publicly available.

A morphological analysis of the galaxy cluster XLSSC 122 at z=1.98

Abstract We present a morphological analysis of 29 spectroscopically confirmed members of XLSSC 122, a massive galaxy cluster at z = 1.98. We perform photometry using Statmorph on images of the cluster members from the Hubble Space Telescope (HST) Wide Field Camera (WFC3) in the F140W band. We visually assess the images and compute non-parametric morphological measures, namely the concentration C, asymmetry A, Gini and M20 values and use them to classify cluster members as either being bulge-dominated, disk-dominated or presenting possible merger features. The morphological properties of the XLSSC 122 members show clear evidence of bimodality. The bulge-dominated galaxies are redder, older and are found in the denser regions of the cluster, while the galaxies showing disturbed features are bluer, younger and are found towards the outskirts of the cluster. XLSSC 122 is also found to be deficient in blue and disturbed galaxies compared to field galaxy populations from the CANDELS/3D-HST surveys. An analysis of merger events occurring in numerical simulations suggest that galaxy interactions generating a population of morphologically disturbed galaxies in XLSSC 122 may have occurred over the interval 2 &amp;lt; z &amp;lt; 3, i.e. prior to their infall into the virial core of the cluster.

A complex node of the cosmic web associated with the massive galaxy cluster MACS J0600.1-2008

ABSTRACT MACS J0600.1-2008 (MACS0600) is an X-ray-luminous, massive galaxy cluster at $z_{\mathrm{d}}=0.43$, studied previously by the REionization LensIng Cluster Survey and ALMA Lensing Cluster Survey projects which revealed a complex, bimodal mass distribution and an intriguing high-redshift object behind it. Here, we report on the results of a combined analysis of the extended strong lensing (SL), X-ray, Sunyaev–Zeldovich (SZ), and galaxy luminosity-density properties of this system. Using new JWST and ground-based Gemini-N and Keck data, we obtain 13 new spectroscopic redshifts of multiply-imaged galaxies and identify 12 new photometric multiple-image systems and candidates, including two multiply-imaged $z\sim 7$ objects. Taking advantage of the larger areal coverage, our analysis reveals an additional bimodal, massive SL structure which we measure spectroscopically to lie adjacent to the cluster and whose existence was implied by previous SL-modelling analyses. While based in part on photometric systems identified in ground-based imaging requiring further verification, our extended SL model suggests that the cluster may have the second-largest critical area and effective Einstein radius observed to date, $A_{\mathrm{crit}}\simeq 2.16\, \mathrm{arcmin}^2$ and $\theta _{\mathrm{E}}=49.7^{\prime \prime }\pm 5.0^{\prime \prime }$ for a source at $z_{\mathrm{s}}=2$, enclosing a total mass of $M(\lt \theta _{\mathrm{E}})=(4.7\pm 0.7)\times 10^{14}\, \mathrm{M}_{\odot }$. These results are also supported by the galaxy luminosity distribution, and the SZ and X-ray data. Yet another, probably related massive cluster structure, discovered in X-rays 5 arcmin (1.7 Mpc) further north, suggests that MACS0600 is part of an even larger filamentary structure. This discovery adds to several recent detections of massive structures around SL galaxy clusters and establishes MACS0600 as a prime target for future high-redshift surveys with JWST.

Diverse Oxygen Abundance in Early Galaxies Unveiled by Auroral Line Analysis with JWST

We present deep JWST NIRSpec observations in the sight line of MACS J1149.5+2223, a massive cluster of galaxies at z = 0.54. We report the spectroscopic redshift of 28 sources at 3 < z < 9.1, including nine sources with the detection of the OIIIλ4363 auroral line. Combining these with 16 OIIIλ4363 -detected sources from publicly available JWST data, our sample consists of 25 galaxies with robust gas-phase metallicity measurements via the direct method. We observe a positive correlation between stellar mass and metallicity, with an ∼0.5 dex offset down below the local relation. Interestingly, we find a larger-than-expected scatter of ∼0.3 dex around the relation, which cannot be explained by redshift evolution among our sample or other third parameters. The scatter increases at higher redshift, and we tentatively attribute this to the enrichment process having higher stochasticity, due to shallower potential wells, more intense feedback processes, and a higher galaxy merger rate. Despite reaching a considerably low-mass regime ( logM*/M⊙∼7.3 ), our samples have metallicity of log(O/H) +12 ≳ 7, i.e., comparable to the most metal-poor galaxies in the local Universe. The search for primordial galaxies may be accomplished by extending toward a lower mass and/or by investigating inhomogeneities at smaller spatial scales. Lastly, we investigate potential systematics caused by the limitation of JWST’s Micro-Shutter Assembly observations. Caution is warranted when the target exceeds the slit size, as this situation could allow an overestimation of global metallicity, especially under the presence of a strong negative metallicity gradient.

The Galaxy–Galaxy Strong Lensing Cross Section and the Internal Distribution of Matter in ΛCDM Substructure

Strong gravitational lensing offers a powerful probe of the detailed distribution of matter in lenses, while magnifying and bringing faint background sources into view. Observed strong lensing by massive galaxy clusters, which are often in complex dynamical states, has also been used to map their dark matter (DM) substructures on smaller scales. Deep high-resolution imaging has revealed the presence of strong lensing events associated with these substructures, namely galaxy-scale sub-halos. However, an inventory of these observed galaxy–galaxy strong lensing (GGSL) events is noted to be discrepant with state-of-the-art ΛCDM simulations. Cluster sub-halos appear to be over-concentrated compared to their simulated counterparts yielding an order-of-magnitude higher value of GGSL. In this paper, we explore the possibility of resolving this observed discrepancy by redistributing the mass within observed cluster sub-halos in ways that are consistent within the ΛCDM paradigm of structure formation. Lensing mass reconstructions from data provide constraints on the mass enclosed within apertures and are agnostic to the detailed mass profile within them. Therefore, as the detailed density profile within cluster sub-halos currently remains unconstrained by data, we are afforded the freedom to redistribute the enclosed mass. We investigate if rearranging the mass to a more centrally concentrated density profile helps alleviate the GGSL discrepancy. We report that refitting cluster sub-halos to the ubiquitous ΛCDM-motivated Navarro–Frenk–White profile, and further modifying them to include significant baryonic components, does not resolve this tension. A resolution to this persisting GGSL discrepancy may require more careful exploration of alternative DM models.

El Gordo needs El Anzuelo: Probing the structure of cluster members with multi-band extended arcs in JWST data

Gravitational lensing by galaxy clusters involves hundreds of galaxies over a large redshift range and increases the likelihood of rare phenomena (supernovae, microlensing, dark substructures, etc.). Characterizing the mass and light distributions of foreground and background objects often requires a combination of high-resolution data and advanced modeling techniques. We present the detailed analysis of a prominent quintuply imaged dusty star-forming galaxy ($ mainly lensed by three members of the massive galaxy cluster ACT-CL\,J0102$-$4915, also known as d =0.87$). We leverage JWST/NIRCam images, which contain lensing features that were unseen in previous HST images, using a Bayesian, multi-wavelength, differentiable and GPU-accelerated modeling framework that combines (lens modeling) and (field model and inference) software packages. For one of the deflectors, we complement lensing constraints with stellar kinematics measured from VLT/MUSE data. In our lens model, we explicitly include the mass distribution of the cluster, locally corrected by a constant shear field. We find that the two main deflectors (L1 and L2) have logarithmic mass density slopes steeper than isothermal, with $ L1 and $ L2 We argue that such steep density profiles can arise due to tidally truncated mass distributions, which we probe thanks to the cluster lensing boost and the strong asymmetry of the lensing configuration. Moreover, our three-dimensional source model captures most of the surface brightness of the lensed galaxy, revealing a clump with a maximum diameter of $400$ parsecs at the source redshift, visible at wavelengths $ rest mu m. Finally, we caution on using point-like features within extended arcs to constrain galaxy-scale lens models before securing them with extended arc modeling.

Weak lensing mass bias and the alignment of centre proxies

ABSTRACT Galaxy cluster masses derived from observations of weak lensing suffer from a number of biases affecting the accuracy of mass-observable relations calibrated from such observations. In particular, the choice of the cluster centre plays a prominent role in biasing inferred masses. In the past, empirical miscentring distributions have been used to address this issue. Using hydrodynamic simulations, we aim to test the accuracy of weak lensing mass bias predictions based on such miscentring distributions by comparing the results to mass biases computed directly using intracluster medium (ICM)-based centres from the same simulation. We construct models for fitting masses to both centred and miscentred Navarro–Frenk–White profiles of reduced shear, and model the resulting distributions of mass bias with normal and lognormal distributions. We find that the standard approach of using miscentring distributions leads to an overestimation of cluster masses at levels of between 2 per cent and 6 per cent when compared to the analysis in which actual simulated ICM centres are used, even when the underlying miscentring distributions match in terms of the miscentring amplitude. While we find that neither lognormal nor normal distributions are generally reliable for accurately modelling the shapes of the mass bias distributions, both models can serve as reasonable approximations in practice.

Neutral hydrogen lensing simulations in the hubble frontier fields

ABSTRACT Cold gas evolution ties the formation of dark matter haloes to the star formation history of the universe. A primary component of cold gas, neutral atomic hydrogen (HI), can be traced by its 21-cm emission line. However, the faintness of this emission typically limits individual detections to low redshifts ($z\lesssim 0.2$). To address this limitation, we investigate the potential of targeting gravitationally lensed systems. Building on our prior galaxy–galaxy simulations, we have developed a ray-tracing code to simulate lensed HI images for known galaxies situated behind the massive hubble frontier field galaxy clusters. Our findings reveal the existence of high HI mass, high HI magnification systems in these cluster-lensing scenarios. Through simulations of hundreds of sources, we have identified compelling targets within the redshift range $z\approx 0.7 - 1.5$. The most promising candidate from our simulations is the Great Arc at z = 0.725 in Abell 370, which should be detectable by MeerKAT in approximately 50 h. Importantly, the derived HI mass is predicted to be relatively insensitive to systematic uncertainties in the lensing model, and should be constrained within a factor of ${\sim }2.5$ for a 95 per cent confidence interval.

LtU-ILI: An All-in-One Framework for Implicit Inference in Astrophysics and Cosmology

This paper presents the Learning the Universe Implicit Likelihood Inference (LtU-ILI) pipeline, a codebase for rapid, user-friendly, and cutting-edge machine learning (ML) inference in astrophysics and cosmology. The pipeline includes software for implementing various neural architectures, training schema, priors, and density estimators in a manner easily adaptable to any research workflow. It includes comprehensive validation metrics to assess posterior estimate coverage, enhancing the reliability of inferred results. Additionally, the pipeline is easily parallelizable, designed for efficient exploration of modeling hyperparameters. To demonstrate its capabilities, we present real applications across a range of astrophysics and cosmology problems, such as: estimating galaxy cluster masses from X-ray photometry; inferring cosmology from matter power spectra and halo point clouds; characterising progenitors in gravitational wave signals; capturing physical dust parameters from galaxy colors and luminosities; and establishing properties of semi-analytic models of galaxy formation. We also include exhaustive benchmarking and comparisons of all implemented methods as well as discussions about the challenges and pitfalls of ML inference in astronomical sciences. All code and examples are made publicly available at https://github.com/maho3/ltu-ili.

Cosmic accretion shocks as a tool to measure the dark matter mass of galaxy clusters

Cosmic accretion shocks as a tool to measure the dark matter mass of galaxy clusters

The heart of galaxy clusters: Demographics and physical properties of cool-core and non-cool-core halos in the TNG-Cluster simulation

We analyzed the physical properties of the gaseous intracluster medium (ICM) at the center of massive galaxy clusters with TNG-Cluster, a new cosmological magnetohydrodynamical simulation. Our sample contains 352 simulated clusters spanning a halo mass range of 1014 &lt; M500c/M⊙ &lt; 2 × 1015 at z = 0. We focused on the proposed classification of clusters into cool-core (CC) and non-cool-core (NCC) populations, the z = 0 distribution of cluster central ICM properties, and the redshift evolution of the CC cluster population. We analyzed the resolved structure and radial profiles of entropy, temperature, electron number density, and pressure. To distinguish between CC and NCC clusters, we considered several criteria: central cooling time, central entropy, central density, X-ray concentration parameter, and density profile slope. According to TNG-Cluster and with no a priori cluster selection, the distributions of these properties are unimodal, whereby CCs and NCCs represent the two extremes. Across the entire TNG-Cluster sample at z = 0 and based on the central cooling time, the strong CC fraction is fSCC = 24%, compared to fWCC = 60% and fNCC = 16% for weak and NCCs, respectively. However, the fraction of CCs depends strongly on both halo mass and redshift, although the magnitude and even direction of the trends vary with definition. The abundant statistics of simulated high-mass clusters in TNG-Cluster enabled us to match observational samples and make a comparison with data. The CC fractions from z = 0 to z = 2 are in broad agreement with observations, as are the radial profiles of thermodynamical quantities, globally as well as when divided as CC versus NCC halos. TNG-Cluster can therefore be used as a laboratory to study the evolution and transformations of cluster cores due to mergers, AGN feedback, and other physical processes.

Scrutinizing evidence for the triggering of active galactic nuclei in the outskirts of massive galaxy clusters at z ≈ 1

ABSTRACT Environmental effects are believed to play an important yet poorly understood role in triggering accretion events onto the supermassive black holes (SMBHs) of galaxies (active galactic nuclei; AGNs). Massive clusters, which represent the densest structures in the Universe, provide an excellent laboratory to isolate environmental effects and study their impact on black hole growth. In this work, we critically review observational evidence for the preferential activation of SMBHs in the outskirts of galaxy clusters. We develop a semi-empirical model under the assumption that the incidence of AGN in galaxies is independent of environment. We demonstrate that the model is broadly consistent with recent observations on the AGN halo occupation at z = 0.2, although it may overpredict satellite AGN in massive haloes at that low redshift. We then use this model to interpret the projected radial distribution of X-ray sources around high redshift (z ≈ 1) massive ($\gt 5 \times 10^{14} \, M_\odot$) clusters, which show excess counts outside their virial radius. Such an excess naturally arises in our model as a result of sample variance. Up to 20 per cent of the simulated projected radial distributions show excess counts similar to the observations, which are however, because of background/foreground AGN and hence, not physically associated with the cluster. Our analysis emphasizes the importance of projection effects and shows that current observations of z ≈ 1 clusters remain inconclusive on the activation of SMBHs during infall.

The FLAMINGO project: Galaxy clusters in comparison to X-ray observations

Abstract Galaxy clusters are important probes for both cosmology and galaxy formation physics. We test the cosmological, hydrodynamical FLAMINGO simulations by comparing to observations of the gaseous properties of clusters measured from X-ray observations. FLAMINGO contains unprecedented numbers of massive galaxy groups (&amp;gt;106) and clusters (&amp;gt;105) and includes variations in both cosmology and galaxy formation physics. We predict the evolution of cluster scaling relations as well as radial profiles of the temperature, density, pressure, entropy, and metallicity for different masses and redshifts. We show that the differences between volume-, and X-ray-weighting of particles in the simulations, and between cool-core non cool-core samples, are similar in size as the differences between simulations for which the stellar and AGN feedback has been calibrated to produce significantly different gas fractions. Compared to thermally-driven AGN feedback, kinetic jet feedback calibrated to produce the same gas fraction at R500c yields a hotter core with higher entropies and lower densities, which translates into a smaller fraction of cool-core clusters. Stronger feedback, calibrated to produce lower gas fractions and hence lower gas densities, results in higher temperatures, entropies, and metallicities, but lower pressures. The scaling relations and thermodynamic profiles show almost no evolution with respect to self-similar expectations, except for the metallicity decreasing with redshift. We find that the temperature, density, pressure, and entropy profiles of clusters in the fiducial FLAMINGO simulation are in excellent agreement with observations, while the metallicities in the core are too high.

Introducing the TNG-Cluster simulation: Overview and the physical properties of the gaseous intracluster medium

We introduce the new TNG-Cluster project, an addition to the IllustrisTNG suite of cosmological magnetohydrodynamical simulations of galaxy formation. Our objective is to significantly increase the statistical sampling of the most massive and rare objects in the Universe: galaxy clusters with log(M200c/M⊙) ≳ 14.3 − 15.4 at z = 0. To do so, we re-simulate 352 cluster regions drawn from a 1 Gpc volume that is 36 times larger than TNG300, keeping the IllustrisTNG physical model entirely fixed as well as the numerical resolution. This new sample of hundreds of massive galaxy clusters enables studies of the assembly of high-mass ellipticals and their supermassive black holes (SMBHs), brightest cluster galaxies (BCGs), satellite galaxy evolution and environmental processes, jellyfish galaxies, intracluster medium (ICM) properties, cooling and active galactic nuclei (AGN) feedback, mergers and relaxedness, magnetic field amplification, chemical enrichment, and the galaxy-halo connection at the high-mass end, with observables from the optical to radio synchrotron and the Sunyaev-Zeldovich (SZ) effect, to X-ray emission, as well as their cosmological applications. We present an overview of the simulation, the cluster sample, select comparisons to data, and a first look at the diversity and physical properties of our simulated clusters and their hot ICM.

The hot circumgalactic media of massive cluster satellites in the TNG-Cluster simulation: Existence and detectability

The most massive galaxy clusters in the Universe host tens to hundreds of massive satellite galaxies M⋆ ∼ 1010 − 12.5 M⊙, but it is unclear if these satellites are able to retain their own gaseous atmospheres. We analyze the evolution of ≈90 000 satellites of stellar mass ∼109 − 12.5 M⊙ around 352 galaxy clusters of mass M200c ∼ 1014.3 − 15.4 M⊙ at z = 0 from the new TNG-Cluster suite of cosmological magneto-hydrodynamical galaxy cluster simulations. The number of massive satellites per host increases with host mass, and the mass–richness relation broadly agrees with observations. A halo of mass M200chost ∼ 1014.5(1015) M⊙ hosts ∼100 (300) satellites today. Only a minority of satellites retain some gas, hot or cold, and this fraction increases with stellar mass. lower-mass satellites ∼109 − 10 M⊙ are more likely to retain part of their cold interstellar medium, consistent with ram pressure preferentially removing hot extended gas first. At higher stellar masses ∼1010.5 − 12.5 M⊙, the fraction of gas-rich satellites increases to unity, and nearly all satellites retain a sizeable portion of their hot, spatially extended circumgalactic medium (CGM), despite the ejective activity of their supermassive black holes. According to TNG-Cluster, the CGM of these gaseous satellites can be seen in soft X-ray emission (0.5−2.0 keV) that is, ≳10 times brighter than the local background. This X-ray surface brightness excess around satellites extends to ≈30 − 100 kpc, and is strongest for galaxies with higher stellar masses and larger host-centric distances. Approximately 10% of the soft X-ray emission in cluster outskirts ≈0.75 − 1.5 R200c originates from satellites. The CGM of member galaxies reflects the dynamics of cluster-satellite interactions and contributes to the observationally inferred properties of the intracluster medium.

Radio relics in massive galaxy cluster mergers in the TNG-Cluster simulation

Radio relics are diffuse synchrotron sources in the outskirts of merging galaxy clusters energized by the merger shocks. In this paper, we present an overview of the radio relics in massive cluster mergers identified in the new TNG-Cluster simulation. This is a suite of magnetohydrodynamical cosmological zoom-in simulations of 352 massive galaxy clusters with M500c = 1014.0 − 15.3 M⊙ sampled from a 1 Gpc-sized cosmological box. The simulations were performed using the moving-mesh code AREPO with the galaxy formation model and high numerical resolution consistent with the TNG300 run of the IllustrisTNG series. We post-processed the shock properties obtained from the on-the-fly shock finder to estimate the diffuse radio emission generated by cosmological shockwaves for a total of ∼300 radio relics at redshift z = 0 − 1. TNG-Cluster returned a variety of radio relics with diverse morphologies, encompassing classical examples of double radio relics, single relics, and “inverted” radio relics that are convex to the cluster center. Moreover, the simulated radio relics reproduced both the abundance and statistical relations of observed relics. We find that extremely large radio relics (&gt; 2 Mpc) are predominantly produced in massive cluster mergers with M500c ≳ 8 × 1014 M⊙. This underscores the significance of simulating massive mergers to study giant radio relics similar to those found in observations. We released a library of radio relics from the TNG-Cluster simulation, which will serve as a crucial reference for upcoming next-generation surveys.