Galaxy Clusters Research Articles

MAMMOTH-Subaru. II. Diverse Populations of Circumgalactic Lyα Nebulae at Cosmic Noon

Circumgalactic Lyα nebulae are gaseous halos around galaxies exhibiting luminous extended Lyα emission. This work investigates Lyα nebulae from deep imaging of ∼12 deg2 sky, targeted by the MAMMOTH-Subaru survey. Utilizing the wide-field capability of Hyper Suprime-Cam, we present one of the largest blind Lyα nebula selections, including QSO nebulae, Lyα blobs, and radio galaxy nebulae down to the typical 2σ Lyα surface brightness of (5-10)×10−18ergs−1cm−2arcsec−2 . The sample contains 117 nebulae with Lyα sizes of 40–400 kpc, and the most gigantic one spans about 365 kpc, and is referred to as the Ivory Nebula. Combining multiwavelength data, we investigate diverse nebula populations and associated galaxies. We find a small fraction of Lyα nebulae have QSOs (∼7%), luminous infrared galaxies (LIRGs; ∼1%), and radio galaxies (∼2%). Remarkably, among the 28 enormous Lyα nebulae (ELANe) exceeding 100 kpc, about 80% are associated with UV-faint galaxies (M UV > −22), and are categorized as Type II ELANe. We underscore that Type II ELANe constitute the majority but remain largely hidden in current galaxy and QSO surveys. Dusty starburst and obscured AGN activity are proposed to explain the nature of Type II ELANe. The spectral energy distribution of stacking all Lyα nebulae also reveals signs of massive dusty star-forming galaxies with obscured AGNs. We propose a model to explain the dusty nature where the diverse populations of Lyα nebulae capture massive galaxies at different evolutionary stages undergoing violent assembly. Lyα nebulae provide critical insights into the formation and evolution of today’s massive cluster galaxies at cosmic noon.

Structure of the Baryon Halo Around a Supermassive Primordial Black Hole

According to some theoretical models, primordial black holes with masses of more than 108 solar masses could be born in the early universe, and their possible observational manifestations have been investigated in a number of works. Dense dark matter and baryon halos could form around such primordial black holes even at the pre-galactic stage (in the cosmological Dark Ages epoch). In this paper, the distribution and physical state of the gas in the halo are calculated, taking into account the radiation transfer from the central accreting primordial black hole. This made it possible to find the ionization radius, outside of which there are regions of neutral hydrogen absorption in the 21 cm line. The detection of annular absorption regions at high redshifts in combination with a central bright source may provide evidence of the existence of supermassive primordial black holes. We also point out the fundamental possibility of observing absorption rings with strong gravitational lensing on galaxy clusters, which weakens the requirements for the angular resolution of radio telescopes.

Self-organization in collisionless, high-β turbulence

The magnetohydrodynamic (MHD) equations, as a collisional fluid model that remains in local thermodynamic equilibrium (LTE), have long been used to describe turbulence in myriad space and astrophysical plasmas. Yet, the vast majority of these plasmas, from the solar wind to the intracluster medium (ICM) of galaxy clusters, are only weakly collisional at best, meaning that significant deviations from LTE are not only possible but common. Recent studies have demonstrated that the kinetic physics inherent to this weakly collisional regime can fundamentally transform the evolution of such plasmas across a wide range of scales. Here, we explore the consequences of pressure anisotropy and Larmor-scale instabilities for collisionless, $\beta \gg 1$ , turbulence, focusing on the role of a self-organizational effect known as ‘magneto-immutability’. We describe this self-organization analytically through a high- $\beta$ , reduced ordering of the Chew–Goldberger–Low-MHD (CGL-MHD) equations, finding that it is a robust inertial-range effect that dynamically suppresses magnetic-field-strength fluctuations, anisotropic-pressure stresses and dissipation due to heat fluxes. As a result, the turbulent cascade of Alfvénic fluctuations continues below the putative viscous scale to form a robust, nearly conservative, MHD-like inertial range. These findings are confirmed numerically via Landau-fluid CGL-MHD turbulence simulations that employ a collisional closure to mimic the effects of microinstabilities. We find that microinstabilities occupy a small ( ${\sim }5\,\%$ ) volume-filling fraction of the plasma, even when the pressure anisotropy is driven strongly towards its instability thresholds. We discuss these results in the context of recent predictions for ion-vs-electron heating in low-luminosity accretion flows and observations implying suppressed viscosity in ICM turbulence.

The cosmological analysis of X-ray cluster surveys. VI. Inference based on analytically simulated observable diagrams

The number density of galaxy clusters across mass and redshift has been established as a powerful cosmological probe, yielding important information on the matter components of the Universe. Cosmological analyses with galaxy clusters traditionally employ scaling relations, which are empirical relationships between cluster masses and their observable properties. However, many challenges arise from this approach as the scaling relations are highly scattered, maybe ill-calibrated, depend on the cosmology, and contain many nuisance parameters with low physical significance. For this paper, we used a simulation-based inference method utilizing artificial neural networks to optimally extract cosmological information from a shallow X-ray survey, solely using count rates, hardness ratios, and redshifts. This procedure enabled us to conduct likelihood-free inference of cosmological parameters $ m $ and $ To achieve this, we analytically generated several datasets of 70\,000 cluster samples with totally random combinations of cosmological and scaling relation parameters. Each sample in our simulation is represented by its galaxy cluster distribution in a count rate (CR) and hardness ratio (HR) space in multiple redshift bins. We trained convolutional neural networks (CNNs) to retrieve the cosmological parameters from these distributions. We then used neural density estimation (NDE) neural networks to predict the posterior probability distribution of $ m $ and $ given an input galaxy cluster sample. Using the survey area as a proxy for the number of clusters detected for fixed cosmological and astrophysical parameters, and hence of the Poissonian noise, we analyze various survey sizes. The 1 sigma errors of our density estimator on one of the target testing simulations are 1\,000\,deg$^2$, 15.2<!PCT!> for $ m $ and 10.0<!PCT!> for $ and 10\,000\,deg$^2$, 9.6<!PCT!> for $ m $ and 5.6<!PCT!> for $ We also compare our results with a traditional Fisher analysis and explore the effect of an additional constraint on the redshift distribution of the simulated samples. We demonstrate, as a proof of concept, that it is possible to calculate cosmological predictions of $ m $ and $ from a galaxy cluster population without explicitly computing cluster masses and even the scaling relation coefficients, thus avoiding potential biases resulting from such a procedure.

The cooler past of the intracluster medium in TNG-Cluster

Abstract The intracluster medium (ICM) today is comprised largely of hot gas with clouds of cooler gas of unknown origin and lifespan. We analyze the evolution of cool gas (temperatures ≲ 104.5 K) in the ICM of 352 galaxy clusters from the TNG-Cluster simulations, with present-day mass ∼1014.3 − 15.4 M⊙. We follow the main progenitors of these clusters over the past ∼13 billion years (since z ≲ 7) and find that, according to TNG-Cluster, the cool ICM mass increases with redshift at fixed cluster mass, implying that this cooler past of the ICM is due to more than just halo growth. The cool cluster gas at z ≲ 0.5 is mostly located in and around satellite galaxies, while at z ≳ 2 cool gas can also accrete via filaments from the intergalactic medium. Lower-mass and higher-redshift clusters are more susceptible to cooling. The cool ICM mass correlates with the number of gaseous satellites and inversely with the central supermassive black hole (SMBH) mass. The average number of gaseous satellites decreases since z = 2, correlating with the decline in the cool ICM mass over cosmic time, suggesting a link between the two. Concurrently, kinetic SMBH feedback shifts the ICM temperature distribution, decreasing the cool ICM mass inside-out. At z ≈ 0.5, the predicted Mg ii column densities are in the ballpark of recent observations, where satellites and other halos contribute significantly to the total Mg ii column density. Suggestively, a non-negligible amount of the ICM cool gas forms stars in-situ at early times, reaching ∼102 M⊙ yr−1 and an Hα surface brightness of ∼10−17 erg s−1 cm−2 arcsec−2 at z ≈ 2, detectable with Euclid and JWST.

Masses of Sunyaev-Zel’dovich galaxy clusters detected by the Atacama Cosmology Telescope: Stacked lensing measurements with Subaru HSC year 3 data

Masses of Sunyaev-Zel’dovich galaxy clusters detected by the Atacama Cosmology Telescope: Stacked lensing measurements with Subaru HSC year 3 data

Forecasting the constraints on optical selection bias and projection effects of galaxy cluster lensing with multiwavelength data

Forecasting the constraints on optical selection bias and projection effects of galaxy cluster lensing with multiwavelength data

Sensitivity Analysis of Simulation-Based Inference for Galaxy Clustering

Abstract Simulation-based inference (SBI) is a promising approach to leverage high fidelity cosmological simulations and extract information from the non-Gaussian, non-linear scales that cannot be modeled analytically. However, scaling SBI to the next generation of cosmological surveys faces the computational challenge of requiring a large number of accurate simulations over a wide range of cosmologies, while simultaneously encompassing large cosmological volumes at high resolution. This challenge can potentially be mitigated by balancing the accuracy and computational cost for different components of the the forward model while ensuring robust inference. To guide our steps in this, we perform a sensitivity analysis of SBI for galaxy clustering on various components of the cosmological simulations: gravity model, halo-finder and the galaxy-halo distribution models (halo-occupation distribution, HOD). We infer the σ8 and Ωm using galaxy power spectrum multipoles and the bispectrum monopole assuming a galaxy number density expected from the luminous red galaxies observed using the Dark Energy Spectroscopy Instrument (DESI). We find that SBI is insensitive to changing gravity model between N-body simulations and particle mesh (PM) simulations. However, changing the halo-finder from friends-of-friends (FoF) to Rockstar can lead to biased estimate of σ8 based on the bispectrum. For galaxy models, training SBI on more complex HOD leads to consistent inference for less complex HOD models, but SBI trained on simpler HOD models fails when applied to analyze data from a more complex HOD model. Based on our results, we discuss the outlook on cosmological simulations with a focus on applying SBI approaches to future galaxy surveys.

Stellar stripping efficiencies of satellites in numerical simulations: the effect of resolution, satellite properties and numerical disruption

Abstract The stellar stripping of satellites in cluster haloes is understood to play an important role in the production of intracluster light. Increasingly, cosmological simulations have been utilised to investigate its origin and assembly. However, such simulations typically model individual galaxies at relatively coarse resolutions, raising concerns about their accuracy. Although there is a growing literature on the importance of numerical resolution for the accurate recovery of the mass loss rates of dark matter (DM) haloes, there has been no comparable investigation into the numerical resolution required to accurately recover stellar mass loss rates in galaxy clusters. Using N-body simulations of satellite galaxies orbiting in a cluster halo represented by a static external potential, we conduct a set of convergence tests in order to explore the role of numerical resolution and force softening length on stellar stripping efficiency. We consider a number of orbital configurations, satellite masses and satellite morphologies. We find that stellar mass resolution is of minor importance relative to DM resolution. Resolving the central regions of satellite DM halos is critical to accurately recover stellar mass loss rates. Poorly resolved DM haloes develop cored inner profiles and, if this core is of comparable size to the stellar component of the satellite galaxy, this leads to significant over-stripping. To prevent this, relatively high DM mass resolutions of around MDM ∼ 106 M⊙, better than those achieved by many contemporary cosmological simulations, are necessary.

The VST ATLAS Quasar Survey – II. Halo mass profiles of galaxies, LRGs and galaxy clusters via quasar and CMB lensing

ABSTRACT We cross-correlate a low-contamination subset of the VST ATLAS $g\lt 22.5$ quasar catalogue with $g\lt 21.5$ galaxy clusters, $r\lt 21$ galaxies and $r\lt 19.5$ luminous red galaxies (LRGs) to probe their halo mass profiles via quasar magnification bias caused by weak lensing. In the case of galaxy clusters, we find that at small scales their mass profiles are well fitted by Navarro, Frenk, and White models with masses within the expected range. For the galaxies, we find consistency with previous Sloan Digital Sky Survey-based results for the galaxy–quasar cross-correlation and the galaxy auto-correlation functions. Disagreement as to whether the cross-correlation results are in tension with $\Lambda$cold dark matter appears due to different assumptions as to whether galaxies trace mass. We conclude that halo occupation distribution (HOD) models fit the galaxy–quasar lensing results better than models where galaxies trace the mass. We further test the cluster and galaxy HOD models in the 2-halo range using the Planck cosmic microwave background (CMB) lensing map, finding that the cross-correlation with both the poorest clusters and the galaxies may be marginally overpredicted by the above HOD models. Finally, we measure the magnification bias of LRGs using both quasar and CMB lensing and find that the observed quasar lensing amplitude may be ${\approx} 2\times$ too high and, on larger scales, the CMB lensing amplitude may be too low to be explained by a standard LRG HOD model.

The Three Hundred project: Estimating the dependence of gas filaments on the mass of galaxy clusters

The Three Hundred project: Estimating the dependence of gas filaments on the mass of galaxy clusters

Mass modeling and kinematics of galaxy clusters in modified gravity

The chameleon screening mechanism has been constrained many a time using dynamic and kinematic galaxy cluster observables. Current constraints are, however, insensitive to different mass components within galaxy clusters and have been mainly focused on a single mass density profile, the Navarro-Frenk-White mass density model. In this work, we extend the study of the Chameleon screening mechanism in galaxy clusters by considering a series of mass density models, namely: generalized-Navarro-Frenk-While, b-Navarro-Frenk-While, Burket, Isothermal and Einasto. The coupling strength (β) and asymptotic value of the chameleon field (ϕ ∞) are constrained by using kinematics analyses of simulated galaxy clusters, generated both assuming General Relativity and a strong chameleon scenario. By implementing a Bayesian analysis we comprehensively show that the biases introduced due to an incorrect assumption of the mass model are minimal. Similarly, we also demonstrate that a spurious detection of evidence for modifications to gravity is highly unlikely when utilizing the kinematics of galaxy clusters.

Constraining the average magnetic field in galaxy clusters with current and upcoming CMB surveys

Galaxy clusters that host radio halos indicate the presence of population(s) of non-thermal electrons. These electrons can scatter low-energy photons of the Cosmic Microwave Background, resulting in the non-thermal Sunyaev-Zeldovich (ntSZ) effect. We measure the average ntSZ signal from 62 radio-halo hosting clusters using the Planck multi-frequency all-sky maps. We find no direct evidence of the ntSZ signal in the Planck data. Combining the upper limits on the non-thermal electron density with the average measured synchrotron power collected from the literature, we place lower limits on the average magnetic field strength in our sample. The lower limit on the volume-averaged magnetic field is 0.01–0.24 μG, depending on the assumed power-law distribution of electron energies. We further explore the potential improvement of these constraints from the upcoming Simons Observatory and Fred Young Submillimeter Telescope (FYST) of the CCAT-prime collaboration. We find that combining these two experiments, the constraints will improve by a factor oftwo, which can be sufficient to rule out some power-law models.

Investigating the Kinematics of Central and Satellite Galaxies Using Normalizing Flows

Galaxy clustering contains information on cosmology, galaxy evolution, and the relationship between galaxies and their dark matter hosts. On small scales, the detailed kinematics of galaxies within their host halos determines the galaxy clustering. In this paper, we investigate the dependence of the central and satellite galaxy kinematics on θ , the intrinsic host halo properties (mass, spin, concentration), cosmology (Ωm, σ 8), and baryonic feedback from active galactic nuclei and supernovae (A AGN1, A AGN2, A SN1, A SN2). We utilize 2000 hydrodynamic simulations in CAMELS run using IllustrisTNG and SIMBA galaxy formation models. Focusing on central and satellite galaxies with M * > 109 M ⊙, we apply neural density estimation (NDE) with normalizing flows to estimate their p(Δr ∣ θ ) and p(Δv ∣ θ ), where Δr and Δv are the magnitudes of the halocentric spatial and velocity offsets. With NDE, we accurately capture the dependence of galaxy kinematics on each component of θ . For central galaxies, we identify significant spatial and velocity biases dependent on halo mass, concentration, and spin. For satellite distributions, we find significant deviations from a Navarro–Frenk–White profile and evidence that they consist of distinct orbiting and infalling populations. However, we find no strong dependence on θ besides a weak dependence on host halo spin. For both central and satellite galaxies, there is no notable dependence on cosmological parameters and baryonic feedback. These results provide key insights for improving the current halo occupation distribution (HOD) models. This work is the first in a series that will reexamine and develop HOD frameworks for improved modeling of galaxy clustering at smaller scales.

Accelerated Structure Formation: The Early Emergence of Massive Galaxies and Clusters of Galaxies

Galaxies in the early Universe appear to have grown too big too fast, assembling into massive, monolithic objects more rapidly than anticipated in the hierarchical Lambda cold dark matter (ΛCDM) structure formation paradigm. The available photometric data are consistent with there being a population of massive galaxies that form early (z ≳ 10) and quench rapidly over a short (≲1 Gyr) timescale, consistent with the traditional picture for the evolution of giant elliptical galaxies. Similarly, kinematic observations as a function of redshift show that massive spirals and their scaling relations were in place at early times. Explaining the early emergence of massive galaxies requires either an extremely efficient conversion of baryons into stars at z > 10 or a more rapid assembly of baryons than anticipated in ΛCDM. The latter possibility was explicitly predicted in advance by modified Newtonian dynamics (MOND). We discuss some further predictions of MOND, such as the early emergence of clusters of galaxies and early reionization.

Confusion of extragalactic sources in the far-infrared: A baseline assessment of the performance of PRIMAger in intensity and polarization

Because of their limited angular resolution, far-infrared telescopes are usually affected by the confusion phenomenon. Since several galaxies can be located in the same instrumental beam, only the brightest objects emerge from the fluctuations caused by fainter sources. The PRobe far-Infrared Mission for Astrophysics imager (PRIMAger) will observe the mid- and far-infrared (25--235\,mu m) sky both in intensity and polarization. We aim to provide predictions of the confusion level and its consequences for future surveys. We produced simulated PRIMAger maps affected only by the confusion noise using the simulated infrared extragalactic sky (SIDES) semi-empirical simulation. We then estimated the confusion limit in these maps and extracted the sources using a basic blind extractor. By comparing the input galaxy catalog and the extracted source catalog, we derived various performance metrics as completeness, purity, and the accuracy of various measurements (e.g., the flux density in intensity and polarization or the polarization angle). In intensity maps, we predict that the confusion limit increases rapidly with increasing wavelength (from 21\,mu Jy at 25\,mu m to 46\,mJy at 235\,mu m). The confusion limit in polarization maps is more than two orders of magnitude lower (from 0.03\,mJy at 96\,mu m to 0.25\,mJy at 235\,mu m). Both in intensity and polarization maps, the measured (polarized) flux density is dominated by the brightest galaxy in the beam, but other objects also contribute in intensity maps at longer wavelengths (sim 30\,<!PCT!> at 235\,mu m). We also show that galaxy clustering has a mild impact on confusion in intensity maps (up to 25\,<!PCT!>), while it is negligible in polarization maps. In intensity maps, a basic blind extraction will be sufficient to detect galaxies at the knee of the luminosity function up to zsim 3 and 1011\,M$_ main-sequence galaxies up to zsim 5. In polarization for the most conservative sensitivity forecast (payload requirements), sim 200 galaxies can be detected up to z=1.5 in two 1\,500\,h surveys covering 1\,deg$^2$ and 10\,deg$^2$. For a conservative sensitivity estimate, we expect sim 8\,000 detections up to z=2.5, opening a totally new window on the high-z dust polarization. Finally, we show that intensity surveys at short wavelengths and polarization surveys at long wavelengths tend to reach confusion at similar depth. There is thus a strong synergy between them.

Forecasting Constraints from Surface Brightness Fluctuations in Galaxy Clusters

Studies of surface brightness (SB) fluctuations in the intracluster medium present an indirect estimate of turbulent pressure support and associated Mach numbers. While high-resolution X-ray spectroscopy can directly constrain line-of-sight gas motions, including those due to turbulence, such observations are relatively expensive and will be limited to nearby, bright clusters. In this respect, SB fluctuations are the most economical means to constrain turbulent motions at large cluster radii across a range of redshifts and masses. To forecast what current and future X-ray and Sunyaev–Zel’dovich facilities may achieve in SB fluctuation studies, I review and synthesize matters of accuracy and precision with respect to calculating power spectra of SB fluctuations, from which turbulent properties are derived. Balancing concerns of power spectrum accuracy and precision across a range of spatial scales, I propose the use of three annuli with [0, 0.4]R 500, [0.4, 1]R 500, and [1, 1.5]R 500. Adopting these three regions, I calculate the uncertainty in the hydrostatic mass bias, σbM , that can be achieved for various instruments in several scenarios. I find that Lynx and AtLAST are competitive in their constraints at R 500, while AtLAST should perform better when constraining σbM at R 200.

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 Vir > 1015 M ⊙ at z = 0 using the smoothed particle magnetohydrodynamics-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 ∼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.

Cosmocnc: A fast, flexible, and accurate framework for galaxy cluster number count likelihood computation

We introduce cosmocnc, a new framework for computing the number count likelihood of galaxy cluster catalogues in a fast, flexible and accurate way. cosmocnc offers three types of likelihoods: an unbinned, a binned, and an extreme value likelihood. It also supports the addition of stacked cluster data, which is modelled consistently with the cluster catalogue. The unbinned likelihood, which is the main focus of the framework, can take an arbitrary number of mass observables as input and deal with several complexities in the data, such as variations in the properties of the cluster observable across the survey footprint, the possibility of different clusters having measurements for different combinations of mass observables, redshift measurement uncertainties, and the presence on unconfirmed detections in the catalogue. If there are more than one mass observables, the unbinned likelihood is computed with a novel approach, the backward convolutional approach. After introducing the framework in detail, we demonstrate its application with synthetic Simons-Observatory-like catalogues, finding excellent agreement between their properties and cosmocnc's predictions and obtaining constraints on cosmological and scaling relation parameters featuring negligible biases. A Python implementation of the cosmocnc framework is publicly available at https://github.com/inigozubeldia/cosmocnc.

Unveiling the shape: A multi-wavelength analysis of the galaxy clusters Abell 76 and Abell 1307

We analyse the dynamical state of the galaxy clusters Abell 76 and Abell 1307 from the optical point of view, presenting a coherent scenario that responds to the X-ray emissions observed in these structures. Our study is based on 231 and 164 spectroscopic redshifts, for the clusters A76 and A1307, respectively, obtained mostly with the Telescopio Nazionale Galileo, and complemented with others collected from the SDSS DR16 spectroscopic database and the literature. We find that A76 and A1307 are two galaxy clusters at z = 0.0390 and 0.0815, respectively, with a velocity dispersion of 650 ± 56 km s−1 and 863 ± 85 km s−1, and they show velocity distributions following, in practice, Gaussian profiles. From our dynamical analysis, X-ray studies and SZ-Planck emission, we obtain a mean total mass M500 = 1.7 ± 0.6 ⋅ 1014 M⊙ and 3.5 ± 1.3 ⋅ 1014 M⊙ for A76 and A1307, respectively. Using the SDSS DR16 photometric database, we find that the spatial distribution of likely cluster members in the case of A76 is very anisotropic, while A1307 shows a compact distribution of galaxies, but it is double peaked and elongated in the south-north direction. Using XMM-Newton X-ray data, we compared the surface brightness maps with galaxy distributions and noticed that both distributions are correlated. We reconstructed the total mass profile and velocity anisotropy of both clusters by analysing the full projected phase space, through the MG-MAMPOSSt code. Our study reveals a slight indication of radial orbits for A76, while A1307 seems to prefer more isotropic orbits in the whole cluster range. In summary, A76 represents a typical young cluster, in an early stage of formation, with a very low X-ray surface brightness but a high temperature showing a very anisotropic galaxy distribution. A1307 is however more consolidated and massive showing in-homogeneous galaxy distribution and an asymmetric X-ray emission, which suggest a scenario characterised by recent minor mergers.