Intracluster Medium Research Articles

Thermal conductivity with bells and whistlers: Suppression of the magnetothermal instability in galaxy clusters

In the hot and dilute intracluster medium (ICM) in galaxy clusters, kinetic plasma instabilities that are excited at the particle gyroradius may play an important role in the transport of heat and momentum, thus affecting the large-scale evolution of these systems. In this paper, we continue our investigation of the effect of whistler suppression of thermal conductivity on the magneto-thermal instability (MTI), which may be active in the periphery of galaxy clusters and may contribute to the observed levels of turbulence. We use a subgrid closure for the heat flux inspired from kinetic simulations and show that MTI turbulence with whistler suppression exhibits a critical transition as the suppression parameter is increased: for modest suppression of the conductivity, the turbulent velocities generated by the MTI decrease accordingly, in agreement with scaling laws found in previous studies of the MTI. However, for suppression above a critical threshold, the MTI loses its ability to maintain equipartition-level magnetic fields through a small-scale dynamo (SSD), and the system enters a ``death-spiral.'' We show that analogous levels of suppression of thermal conductivity with a simple model of flat uniform suppression would not inhibit the dynamo. We propose a model to explain this critical transition, and speculate that conditions in the hot ICM are such that in substantial portions of the galaxy cluster periphery the MTI might struggle to sustain its own dynamo. We then look at spatial correlations and energy transfers in spectral space and find that, with whistler suppression, most of the heat is transported along thin bundles of strong magnetic fields (the Autobahns of electrons), while high-beta regions are brought out of thermal equilibrium. We link this behavior to the intermittent nature of magnetic fields, and we observe an overall reduction of the efficiency of MTI turbulent driving at the largest turbulent scales. Finally, we show that external turbulence interferes with the MTI and leads to reduced levels of MTI turbulence. While individually both external turbulence and whistler suppression reduce MTI turbulence, we find that they can exhibit a complex interplay when acting in conjunction, with external turbulence boosting the whistler-suppressed thermal conductivity and even reviving a ``dead'' MTI. Our study illustrates how extending magnetohydrodynamics with a simple prescription for microscale plasma physics can lead to the formation of a complicated dynamical system and demonstrates that further work is needed in order to bridge the gap between micro- and macro scales in galaxy clusters.

Observational Predictions for the Survival of Atomic Hydrogen in Simulated Fornax-like Galaxy Clusters

The presence of dense, neutral hydrogen clouds in the hot, diffuse intragroup and intracluster (IC) medium is an important clue to the physical processes controlling the survival of cold gas and sheds light on cosmological baryon flows in massive halos. Advances in numerical modeling and observational surveys mean that theory and observational comparisons are now possible. In this paper, we use the high-resolution TNG50 cosmological simulation to study the H i distribution in seven halos with masses similar to the Fornax galaxy cluster. Adopting observational sensitivities similar to the MeerKAT Fornax Survey (MFS), an ongoing H i survey that will probe to column densities of 1018 cm−2, we find that Fornax-like TNG50 halos have an extended distribution of neutral hydrogen clouds. Within 1 R vir, we predict the MFS will observe a total H i covering fraction of ∼12% (mean value) for 10 kpc pixels and 6% for 2 kpc pixels. If we restrict this to gas more than 10 half-mass radii from galaxies, the mean values only decrease mildly, to 10% (4%) for 10 (2) kpc pixels (albeit with significant halo-to-halo spread). Although there are large amounts of H i outside of galaxies, the gas seems to be associated with satellites, judging both by the visual inspection of projections and by comparison of the line of sight velocities of galaxies and IC H i.

The first high-redshift cavity power measurements of cool-core galaxy clusters with the International LOFAR Telescope

Radio-mode feedback associated with the active galactic nuclei (AGNs) at the cores of galaxy clusters injects a large amount of energy into the intracluster medium (ICM), offsetting radiative losses through X-ray emission. This mechanism prevents the ICM from rapidly cooling down and fueling extreme starburst activity as it accretes onto the central galaxies, and it is therefore a key ingredient in the evolution of galaxy clusters. However, the influence and mode of feedback at high redshifts (z ∼ 1) remains largely unknown. Low-frequency sub-arcsecond-resolution radio observations taken with the International LOFAR Telescope have demonstrated their ability to assist X-ray observations with constraining the energy output from the AGNs (or “cavity power”) in galaxy clusters, thereby enabling research at higher redshifts than before. In this pilot project, we tested this hybrid method on a high-redshift (0.6 < z < 1.3) sample of 13 galaxy clusters for the first time with the aim of verifying the performance of this method at these redshifts and providing the first estimates of the cavity power associated with the central AGN for a sample of distant clusters. We were able to detect clear radio lobes in three out of 13 galaxy clusters at redshifts of 0.7 < z < 0.9, and we used these detections in combination with ICM pressures surrounding the radio lobes obtained from standard profiles to calculate the corresponding cavity powers of the AGNs. Combining our results with the literature, the current data appear to suggest that the average cavity power peaked at a redshift of z ∼ 0.4 and slowly decreases toward higher redshifts. However, we require more and tighter constraints on the cavity volume and a better understanding of our observational systematics to confirm any deviation of the cavity power trend from a constant level.

Cosmic-ray confinement in radio bubbles by micromirrors

ABSTRACT Radio bubbles, ubiquitous features of the intracluster medium around active galactic nuclei, are known to rise buoyantly for multiple scale heights through the intracluster medium (ICM). It is an open question how the bubbles can retain their high-energy cosmic-ray content over such distances. We propose that the enhanced scattering of cosmic rays due to micromirrors generated in the ICM is a viable mechanism for confining the cosmic rays within bubbles and can qualitatively reproduce their morphology. We discuss the observational implications of such a model of cosmic-ray confinement.

The SRG/eROSITA All-Sky Survey. View of the Virgo Cluster

As the closest galaxy cluster, the Virgo Cluster is an exemplary environment for the study of the large-scale filamentary structure and physical effects that are present in cluster outskirts but absent from the more easily studied inner regions. Here, we present an analysis of the SRG/eROSITA data from five all-sky surveys. eROSITA allows us to resolve the entire Virgo cluster and its outskirts on scales between 1 kpc and 3 Mpc, covering a total area on the sky of about 25$^ by 25$^ We utilized image manipulation techniques and surface brightness profiles to search for extended emission, surface brightness edges, and features in the outskirts. We employed a method of comparing mean and median profiles to measure gas clumping out to and beyond the virial radius. Surface brightness analysis of the cluster and individual sectors of the cluster reveal the full extent of previously identified cold fronts to the north and south. The emissivity bias due to gas clumping, which we quantify over three orders of magnitude in the radial range, is found to be mild, consistent with previous findings. We find uniform clumping measurements in all directions, with no enhancements along candidate filaments. We find an estimated virial gas mass of $M_ gas r<r_ $\,M$_ Through imaging analysis we detect the presence of extended emission spanning 320\,kpc to the southwest of M49. The extension has a significance of 3.15sigma and is coincident with radio emission detected with LOFAR, which could be evidence of an accretion shock or turbulent reacceleration as the M49 group or background W' cloud falls into the cluster and interacts with the intracluster medium.

Simba-C: the evolution of the thermal and chemical properties in the intragroup medium

ABSTRACT The newly updated GIZMO and Simba based simulation, Simba-C, with its new stellar feedback, chemical enrichment, and recalibrated AGN feedback, allows for a detailed study of the intragroup medium X-ray properties. We discuss the impact of various physical mechanisms, e.g. stellar and AGN feedback, and chemical enrichment, on the composition and the global scaling relations of nearby galaxy groups. We also study the evolution (z = 2 to 0) of the global properties for the $1\, \mathrm{keV}$ temperature groups. Simba-C shows improved consistent matching with the observations of all X-ray scaling relations compared to Simba. It is well known that AGN feedback has a significant influence on LX, 0.5–2.0–Tspec, corr, S500/2500–Tspec, corr, and gas mass fractions, with our Simba-C results consistent with it. Our recalibrated AGN feedback strength also showed an additional improvement in gas entropy, which now aligns with CLoGS observations. The updated stellar feedback and chemical enrichment model is shown to play an important role in our understanding of the chemical abundance ratios and their evolution within galaxy groups. In particular, we find that Simba-C produces an increase in the amount of heavier elements (specifically Si and Fe) relative to O, compared to Simba.

Atacama Large Aperture Submillimeter Telescope (AtLAST) science: Resolving the hot and ionized Universe through the Sunyaev-Zeldovich effect

An omnipresent feature of the multi-phase “cosmic web” — the large-scale filamentary backbone of the Universe — is that warm/hot (≳ 105 K) ionized gas pervades it. This gas constitutes a relevant contribution to the overall universal matter budget across multiple scales, from the several tens of Mpc-scale intergalactic filaments, to the Mpc intracluster medium (ICM), all the way down to the circumgalactic medium (CGM) surrounding individual galaxies, on scales from ∼ 1 kpc up to their respective virial radii (∼ 100 kpc). The study of the hot baryonic component of cosmic matter density represents a powerful means for constraining the intertwined evolution of galactic populations and large-scale cosmological structures, for tracing the matter assembly in the Universe and its thermal history. To this end, the Sunyaev-Zeldovich (SZ) effect provides the ideal observational tool for measurements out to the beginnings of structure formation. The SZ effect is caused by the scattering of the photons from the cosmic microwave background off the hot electrons embedded within cosmic structures, and provides a redshift-independent perspective on the thermal and kinematic properties of the warm/hot gas. Still, current and next-generation (sub)millimeter facilities have been providing only a partial view of the SZ Universe due to any combination of: limited angular resolution, spectral coverage, field of view, spatial dynamic range, sensitivity, or all of the above. In this paper, we motivate the development of a wide-field, broad-band, multi-chroic continuum instrument for the Atacama Large Aperture Submillimeter Telescope (AtLAST) by identifying the scientific drivers that will deepen our understanding of the complex thermal evolution of cosmic structures. On a technical side, this will necessarily require efficient multi-wavelength mapping of the SZ signal with an unprecedented spatial dynamic range (from arcsecond to degree scales) and we employ detailed theoretical forecasts to determine the key instrumental constraints for achieving our goals.

Differential reddening in 48 globular clusters: An end to the quest for the intracluster medium

For decades, it has been theorized that a tenuous but detectable intracluster medium should be present in globular clusters, which is continuously replenished by the gas and dust ejected by bright giants and periodically cleared by interactions with the Galactic disk. However, dedicated searches, especially in infrared and radio wavelengths, have returned mostly upper limits, which are lower than theoretical expectations by several orders of magnitude. We profited from recent wide-field photometry for 48 Galactic globular clusters to compute high-resolution maps of differential reddening, which can be used to correct any photometric catalog in these areas for reddening variations. Using 3D reddening maps from the literature, we evaluated the amount of foreground extinction. This allowed us to estimate the masses of the intracluster medium in our sample clusters, with an accuracy of one order of magnitude. Our estimates agree with the few available literature detections and with theoretical expectations. Because the discrepancy between observations and expectations only concerns literature upper limits, we explored possible reasons why they could be underestimated and we show that two recent discoveries can explain the discrepancy. The first is the recent discovery that the intracluster medium in 47 Tuc is not centrally concentrated. This is also supported by our maps, which in the majority of cases do not show a central reddening concentration. The second is the discovery that the dust in metal-poor ([Fe/H] ≲ −1 dex) globular clusters is dominated by iron grains rather than silicates, which undermines previous dust mass estimates from observed upper limits. We conclude that current evidence, including our maps, does not contradict theoretical expectations and the problem of the missing intracluster medium is no longer an issue.

The Relation between the Cool-core Radius and the Host Galaxy Clusters: Thermodynamic Properties and Cluster Mass

We present a detailed study of cool-core systems in a sample of four galaxy clusters (RXCJ1504.1-0248, A3112, A4059, and A478) using archival X-ray data from the Chandra X-ray Observatory. Cool cores are frequently observed at the centers of galaxy clusters and are considered to be formed by radiative cooling of the intracluster medium (ICM). Cool cores are characterized by a significant drop in the ICM temperature toward the cluster center. We extract and analyze X-ray spectra of the ICM to measure the radial profiles of the ICM thermodynamic properties, including temperature, density, pressure, entropy, and radiative cooling time. We define the cool-core radius as the turnover radius in the ICM temperature profile and investigate the relation between the cool-core radius and the properties of the host galaxy clusters. In our sample, we observe that the radiative cooling time of the ICM at the cool-core radius exceeds 10 Gyr, with RXCJ1504.1-0248 exhibiting a radiative cooling time of 32−11+5 Gyr at its cool-core radius. These results indicate that not only radiative cooling but also additional mechanisms, such as gas sloshing, may play an important role in determining the size of cool cores. Additionally, we might find that the best-fit relation between the cool-core radius and the cluster mass (M 500) is consistent with a linear relation. Our findings may suggest that cool cores are linked to the evolution of their host galaxy clusters.

X-ray-inferred kinematics of the core intracluster medium in Perseus-like clusters: Insights from the TNG-Cluster simulation

The intracluster medium (ICM) of galaxy clusters encodes the impact of the physical processes that shape these massive halos, including feedback from central supermassive black holes (SMBHs). In this study, we examine the gas thermodynamics, kinematics, and the effects of SMBH feedback on the core of Perseus-like galaxy clusters with a new simulation suite: TNG-Cluster. We first make a selection of simulated clusters similar to Perseus based on the total mass and inner ICM properties, such as their cool-core nature. We identify 30 Perseus-like systems among the 352 TNG-Cluster halos at z = 0. Many exhibit thermodynamical profiles and X-ray morphologies with disturbed features such as ripples, bubbles, and shock fronts that are qualitatively similar to X-ray observations of Perseus. To study observable gas motions, we generate XRISM mock X-ray observations and conduct a spectral analysis of the synthetic data. In agreement with existing Hitomi measurements, TNG-Cluster predicts subsonic gas turbulence in the central regions of Perseus-like clusters, with a typical line-of-sight velocity dispersion of 200 km s−1. This implies that turbulent pressure contributes < 10% to the dominant thermal pressure. In TNG-Cluster, such low (inferred) values of ICM velocity dispersion coexist with high-velocity outflows and bulk motions of relatively small amounts of super-virial hot gas, moving up to thousands of km s−1. However, detecting these outflows in observations may prove challenging due to their anisotropic nature and projection effects. Driven by SMBH feedback, such outflows are responsible for many morphological disturbances in the X-ray maps of cluster cores. They also increase both the inferred and intrinsic ICM velocity dispersion. This effect is somewhat stronger when velocity dispersion is measured from higher-energy lines.

Gas metallicity of ram-pressure-stripped galaxies at intermediate redshifts with MUSE data

Extraplanar tails of ionized-stripped gas, extending up to several tens of kiloparsecs beyond the stellar disk, are often observed in ram-pressure-stripped (RPS) galaxies in low-redshift clusters. Recent studies have also identified similar tails at high redshifts, and we present here the first analysis of the chemical composition of such tails beyond the local Universe. Specifically, we examined the distribution of the ionized gas metallicity of RPS galaxies in the Abell 2744 (z = 0.308) and Abell 370 (z = 0.375) clusters observed as part of the MUSE-GTO program. We investigated spatially resolved and global metallicities in galactic disks and stripped tails, utilizing both a theoretical calibration from a photoionization model and an empirical calibration. The metallicity gradients and the spatially resolved mass–metallicity relations indicate that the metallicity in the tails reaches values that are up to ∼0.6 dex lower than anywhere in the parent disks, with a few exceptions. Both the disks and tails follow a global mass–metallicity relation, though the tail metallicity is systematically lower than that of the corresponding disk, by up to ∼0.2 dex. These findings demonstrate that additional processes are at play in the tails and are consistent with a scenario of a progressive dilution of the metallicity along the tails due to the mixing of the intracluster medium and interstellar gas, in accordance with previous low-z results. In principle, the same scenario can also explain the flat or positive metallicity gradients observed in low-mass RPS galaxies since in these galaxies the interstellar medium’s metallicity can approach the metallicity levels found in the intracluster medium.

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.

Imprints of the internal dynamics of galaxy clusters on the Sunyaev–Zeldovich effect

Context. Forthcoming measurements of the Sunyaev–Zeldovich (SZ) effect in galaxy clusters will dramatically improve our understanding of the main intra-cluster medium (ICM) properties and how they depend on the particular thermal and dynamical state of the associated clusters. Aims. Using a sample of simulated galaxy clusters, whose dynamical history can be well known and described, we assess the impact of the ICM internal dynamics on both the thermal and kinetic SZ effects (tSZ and kSZ, respectively). Methods. We produced synthetic maps of the SZ effect, both thermal and kinetic, for the simulated clusters obtained in a cosmological simulation produced by a cosmological adaptive mesh refinement code. For each galaxy cluster in the sample, its dynamical state is estimated by using a combination of well-established indicators. We used the correlations between SZ maps and cluster dynamical state to look for the imprints of the evolutionary events, mainly mergers, on the SZ signals. Results. While the tSZ effect only shows dependency on dynamical state in its radial distribution, the kinetic effect shows a remarkable correlation with this property: unrelaxed clusters present a higher radial profile and an overall stronger signal at all masses and radii. The reason for this correlation is the fuzziness of the ICM produced by recent merging episodes. Furthermore, the kSZ signal is correlated with rotation for relaxed clusters, while for the disturbed systems, the effect is dominated by other motions such as bulk flows, turbulence, and so on. The kSZ effect shows a dipolar pattern when averaging over cluster dynamical classes, especially for the relaxed population. This feature can be exploited to stack multiple kSZ maps in order to recover a stronger dipole signal that would be correlated with the global rotation properties of the sample. Conclusions. The SZ effect can be used as a tool to estimate the dynamical state of galaxy clusters, especially to segregate those clusters with a quiescent evolution from those with a rich record of recent merger events. Our results suggest that the forthcoming observational data measuring the SZ signal in clusters could be used as a complementary strategy for classifying the evolutionary history of galaxy clusters.

Observed abundance of X-ray low surface brightness clusters in optical, X-ray, and SZ selected samples

The comparison of the properties of galaxy cluster samples selected using observations in different wavebands may shed light on potential biases of the way in which the samples are assembled. For this comparison, we introduce a new observable that does not require previous knowledge of the cluster mass: the X-ray mean surface brightness within the central 300 kpc. We found that clusters with low surface brightness, defined as those with a mean surface brightness below 43.35 erg s−1 Mpc−2, are about one quarter of the whole cluster population in a sample of 32 clusters in the nearby Universe, selected independently of the intracluster medium properties. Almost no example of a low central surface brightness cluster exists instead in two X-ray selected samples, one sample based on XMM-Newton XXL-100 survey data and the other on full-depth eROSITA eFEDS data, although these clusters are known to exist in the range of redshift and mass as probed by these two surveys. Furthermore, the Sunayev–Zeldovich Atacama Cosmology Telescope cluster survey is even more selective than the previous two samples because it does not even include clusters with intermediate surface brightness, which are instead present in X-ray selected samples that explore the same volume of the Universe. Finally, a measure of the mean surface brightness, which is obtained without knowledge of the mass, proves to be effective in narrowing the number of clusters to be followed-up because it recognizes those with a low gas fraction or with a low X-ray luminosity for their mass. Identifying these would otherwise require knowledge of the mass for all clusters.

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.

CHEX-MATE: Robust reconstruction of temperature profiles in galaxy clusters with XMM-Newton

The “Cluster HEritage project with XMM-Newton: Mass Assembly and Thermodynamics at the End point of structure formation” (CHEX-MATE) is a multi-year heritage program to obtain homogeneous XMM-Newton observations of a representative sample of 118 galaxy clusters. The observations are tuned to reconstruct the distribution of the main thermodynamic quantities of the intra-cluster medium up to R500 and to obtain individual mass measurements, via the hydrostatic-equilibrium equation, with a precision of 15−20%. Temperature profiles are a necessary ingredient for the scientific goals of the project and it is thus crucial to derive the best possible temperature measurements from our data. This is why we have built a new pipeline for spectral extraction and analysis of XMM-Newton data, based on a new physically motivated background model and on a Bayesian approach with Markov chain Monte Carlo methods, which we present in this paper for the first time. We applied this new method to a subset of 30 galaxy clusters representative of the CHEX-MATE sample and show that we can obtain reliable temperature measurements up to regions where the source intensity is as low as 20% of the background, keeping systematic errors below 10%. We compare the median profile of our sample and the best-fit slope at large radii with literature results and we find a good agreement with other measurements based on XMM-Newton data. Conversely, when we exclude the most contaminated regions, where the source intensity is below 20% of the background, we find significantly flatter profiles, in agreement with predictions from numerical simulations and independent measurements with a combination of Sunyaev–Zeldovich and X-ray imaging data.

Toward mapping turbulence in the intra-cluster medium

Context. Future X-ray observatories with high spectral resolution and imaging capabilities will enable measurements and mappings of emission line shifts in the intracluster medium (ICM). Such direct measurements can serve as unique probes of turbulent motions in the ICM. Determining the level and scales of turbulence will improve our understanding of the galaxy cluster dynamical evolution and assembly, together with a more precise evaluation of the non thermal support pressure budget. This will allow for more accurate constraints to be placed on the masses of galaxy clusters, among other potential benefits. Aims. In this view, we implemented the methods presented in the previous instalments of our work to characterising the turbulence in the intra-cluster medium in a feasibility study with the X-ray Integral Field Unit (X-IFU) on board the future European X-ray observatory, Athena. Methods. From idealized mock observations of a toy model cluster, we reconstructed the second-order structure function built with the observed velocity field to constrain the turbulence. We carefully accounted for the various sources of errors to derive the most realistic and comprehensive error budget within the limits of our approach. With prior assumptions on the dissipation scale and power spectrum slope, we constrained the parameters of the turbulent power spectrum model through the use of Markov chain Monte Carlo (MCMC) sampling. Results. With a very long exposure time, a favourable configuration, and a prior assumption of the dissipation scale, we were able to retrieve the injection scale, velocity dispersion, and power spectrum slope, with 1σ uncertainties for better than ∼15% of the input values. We demonstrated the efficiency of our carefully set framework to constrain the turbulence in the ICM from high-resolution X-ray spectroscopic observations, paving the way for more in-depth investigation of the optimal required observing strategy within a more restrictive observational setup with the future Athena/X-IFU instrument.

A “MeerKAT-meets-LOFAR” study of the complex multi-component (mini-)halo in the extreme sloshing cluster Abell 2142

Context. Clusters of galaxies are known to be turbulent environments, whether they are merging systems where turbulence is injected via the conversion of gravitational potential energy into the intracluster medium (ICM), or whether they are relaxed systems in which small-scale core sloshing is occurring within the potential well. In many such systems, diffuse radio sources associated with the ICM are found: radio haloes and mini-haloes. Aims. Abell 2142 is a rich cluster undergoing an extreme episode of core sloshing, which has given rise to four cold fronts and a complex multi-component radio halo. Recent work revealed that there are three primary components to the halo that spans a distance of up to around 2.4 Mpc. The underlying physics of particle acceleration on these scales is poorly explored, and requires high-quality multi-frequency data with which to perform precision spectral investigation. We aim to perform such an investigation. Methods. We used new deep MeerKAT L-band (1283 MHz) observations in conjunction with LOFAR HBA (143 MHz) data as well as X-ray data from XMM-Newton and Chandra to study the spectrum of the halo and the connection between the thermal and non-thermal components of the ICM. Results. We confirm the presence of the third halo component, detecting it for the first time at 1283 MHz and confirming its ultra-steep spectrum nature, as we recovered an integrated spectrum of αH3, total = −1.68 ± 0.10. All halo components follow power-law spectra with increasingly steep spectra moving towards the cluster outskirts. We profiled the halo in three directions, finding evidence of asymmetry and spectral steepening along an axis perpendicular to the main axis of the cluster. Our investigation of the thermal non-thermal connection shows sub-linear correlations that are steeper at 1283 MHz than 143 MHz, and we find evidence of different connections in different components of the halo. In particular, we find both a moderate anti-correlation (H1, the core) and positive correlation (H2, the ridge) between the radio spectral index and X-ray temperature. Conclusions. Our results are broadly consistent with an interpretation of turbulent (re-)acceleration following an historic minor cluster merger scenario in which we must invoke some inhomogeneities. However, the anti-correlation between the radio spectral index and X-ray temperature in the cluster core is more challenging to explain; the presence of three cold fronts and a generally lower temperature may provide the foundations of an explanation, but detailed modelling is required to study this further.

Sloshing cold fronts in galaxy cluster Abell 2566

This paper presents properties of the intracluster medium (ICM) in the environment of a cool core cluster Abell 2566 (redshift z= 0.08247) based on the analysis of 20 ks Chandra X-ray data. 2D imaging analysis of the Chandra data from this cluster revealed spiral structures in the morphology of X-ray emission from within the central 109 kpc formed due to gas sloshing. This analysis also witness sharp edges in the surface brightness distribution along the south-east and north-west of the X-ray peaks at 41.6 kpc and 77.4 kpc, respectively. Spectral analysis of 0.5 – 7 keV X-ray photons along these discontinuities exhibited sharp temperature jumps from 2.3 to 3.1 keV and 1.8 to 2.8 keV, respectively, with consistency in the pressure profiles, implying their association with cold fronts due to gas sloshing of the gas. Further confirmation for such an association was provided by the deprojected broken power-law density function fit to the surface brightness distribution along these wedge shaped sectorial regions. This study also witness an offset of 4.6′′(6.8 kpc) between the BCG and the X-ray peak, and interaction of the BCG with a sub-system in the central region, pointing towards the origin of the spiral structure due to a minor merger.

Ram pressure stripping in clusters: gravity can bind the ISM but not the CGM

ABSTRACT We explore the survival of a galaxy’s circumgalactic medium (CGM) as it experiences ram pressure stripping (RPS) moving through the intracluster medium (ICM). For a satellite galaxy, the CGM is often assumed to be entirely stripped/evaporated, an assumption that may not always be justified. We carry out 3D-hydrodynamic simulations of the interstellar and circumgalactic media (ISM + CGM) of a galaxy like JO201 moving through the ICM. The CGM can survive long at cluster outskirts ($\gtrsim 2 \rm \ Gyr$) but at smaller clustercentric distances, 90 per cent of the CGM mass is lost within ∼500 Myr. The gravitational restoring force on the CGM is mostly negligible and the CGM–ICM interaction is analogous to ‘cloud–wind interaction’. The CGM stripping time-scale does not depend on the ram pressure but on the CGM to ICM density contrast χ. Two distinct regimes emerge for CGM stripping: the χ > 1 regime, which is the well-known ‘cloud crushing’ problem, and the χ < 1 regime, which we refer to as the (relatively unexplored) ‘bubble drag’ problem. The first pericentric passage near the cluster core can rapidly – over a crossing time tdrag ∼ R/vrel – strip the CGM in the bubble drag regime. The ISM stripping criterion unlike the CGM criterion, still depends on the ram pressure $\rho _{\rm ICM} v_{\rm rel}^2$. The stripped tails of satellites contain contributions from both the disc and the CGM. The X-ray plume in M89 in the Virgo cluster and a lack of it in the nearby M90 might be attributed to their orbital histories. M90 has likely undergone stripping in the bubble drag regime due to a pericentric passage close to the cluster centre.