arXiv subjects

G. W. Pratt

Publications and source records attributed to G. W. Pratt.

At least 19 recordsLinked to original sources

arXiv2026

Euclid: Galaxy cluster detection through the weak lensing effect - algorithm assessment and selection

Weak gravitational lensing offers a powerful way to detect galaxy clusters by directly tracing their total matter content. Its effectiveness increases with the density of background galaxies, a requirement that is now being met by the high sensitivity and wide coverage of current large-area surveys. A prime example is the Euclid telescope, which will map approximately 14 000 deg2 of the sky, measuring the shapes of billions of galaxies and opening a meaningful window for detecting galaxy clusters uniquely through their weak lensing signal. We present the results of nine galaxy cluster detection algorithms in a blind challenge, using 1200 deg2 of Euclid-like weak lensing observations from the DEMNUni-Cov simulations. The performance of these methods was assessed by matching their detections to known synthetic clusters with signal-to-noise ratios greater than 2, satisfying the z-M selection cut, and adopting two different matching procedures. The purpose of the challenge was to identify and improve strategies for galaxy cluster detection via weak lensing for the upcoming Euclid data releases. We pre-selected four methods based on their individual performance and complementarity. Each pre-selected method adopts a distinct approach: AMICO-WL uses an optimal filtering technique, DoG employs Gaussian filtering, O21 relies on aperture-mass filtering, and W234 applies multi-scale wavelet filtering. Together, the results of these methods can be merged to enhance the processing of Euclid data. Individually, these algorithms reach approximately 10% completeness for a mean purity of 90%, while their combination leads to roughly a two-fold improvement in overall performance, exceeding 70% completeness for low-redshift, high-mass clusters. When extrapolating the results of this work to Euclid Data Release 1, we expect to detect approximately 2500 galaxy clusters via weak gravitational lensing.

astro-ph.CO↗

arXiv2026

Euclid preparation. XCI. Validation method for the detections in the Euclid Catalogue of Galaxy Clusters using external data

We present our methodology for identifying known clusters as counterparts to objects in the Euclid Catalogue of Galaxy Clusters (ECGC). Euclid is expected to detect a large number of optically-selected galaxy clusters over the approximately 14000 square degrees of its extragalactic sky survey. Extending out well beyond redshift unity, the catalogue will contain many new high-redshift clusters, while at lower redshifts a fraction of the clusters will have been observed in other surveys. Identifying these known clusters as counterparts to the Euclid-detected clusters is an important step in the validation and construction of the ECGC to augment information with external observables. We present a set of catalogues and meta-catalogues of known clusters that we have assembled for this step, and we illustrate their application and our methodology using the Dark Energy Survey Year 1 RedMaPPer cluster catalogue in lieu of the future ECGC. In the process of this work, we have constructed and delivered an updated EC-RedMaPPer catalogue with multi-wavelength counterparts.

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arXiv2026

The plethora of diffuse emission in Abell 2034 as revealed by MeerKAT polarization observations

We present MeerKAT observations of the galaxy cluster Abell 2034, a massive (M_500=5.21 10^14 solar masses) nearby cluster in a merging state. Previous observations at 144 MHz have shown that the cluster exhibits a plethora of diffuse emission, with multiple diffuse sources of uncertain classification because of the lack of spectral and polarimetric observations. MeerKAT multi-frequency observations, centered at 816 MHz and 1.28 GHz, together with archival low-frequency LOFAR observations at 144 MHz have allowed us to shed light on the properties of these sources. The polarization properties and spectral index information let us conclude that the cluster hosts one radio relic, a source with a very steep spectrum, previously classified as candidate relic, and filaments of very steep emission around the tailed radio galaxies identified at low frequencies. The presence of a radio halo is confirmed, and its spectrum shows hints for curvature between 144 MHz ad 1.28 GHz. The polarimetric data in the L-band, together with the model of the gas density derived from X-ray observations are used to constrain the magnetic field in the intracluster medium. We assume a radially symmetric magnetic field model, whose strength declines with the cluster gas density as B(r) ~ n_e(r)^0.5, and normalize its strength within R_500. We find that B_500=1 muG best explains the Faraday depth properties of the cluster, though the detection of sources close to the cluster center would be crucial to discriminate among different values. We conclude that the cluster Abell 2034 shows diffuse emission with complex morphologies that do not follow the historical categories of halos and relics. Deep multi-frequency and polarimetric observations are fundamental to understand their origin.

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arXiv2026

Radio Halos in Galaxy Clusters as unveiled by the SKA telescope

Giant radio halos (RHs) are diffuse, Mpc-scale synchrotron sources observed in a growing fraction of galaxy clusters. They trace relativistic particles and magnetic fields in the intracluster medium (ICM), providing a unique window into non-thermal processes and their role in cluster evolution. RHs are primarily found in merging systems, supporting models in which turbulence generated during cluster collisions re-accelerates pre-existing electrons to the energies required for the observed radio emission. In this scenario, the occurrence, power, and spectral properties of RHs depend on the energetics of cluster mergers, with the most massive and dynamically disturbed clusters hosting the most powerful halos. Low-frequency observations are crucial to uncover ultra-steep-spectrum RHs, a key prediction of turbulent re-acceleration models, and are expected to arise from less energetic merger events. LOFAR has enabled statistical studies of large cluster samples, placing robust constraints on RH occurrence and spectral trends. In this Chapter, we model RH formation and evolution using Monte Carlo simulations calibrated on LoTSS-DR2 findings, and we present predictions for SKA-Low in the AA4 configuration. Our results show that SKA will probe an unprecedented region of cluster mass and redshift space, detecting at least $\sim 2500$ RHs up to $z \approx 0.6$, including $\gtrsim 1000$ ultra-steep-spectrum systems, and revealing halos in clusters down to $\sim 10^{14}\, M_\odot$ and out to $z \approx 1$. These surveys will provide stringent tests of turbulent re-acceleration models and significantly advance our understanding of non-thermal processes in galaxy clusters.

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arXiv2026

PSZ: The meta-catalogue of Planck Sunyaev-Zeldovich sources

We present the PSZ, a meta-catalogue of 1962 clusters and cluster candidates produced by the Planck Collaboration. The PSZ contains fully-updated validation information for all official Planck catalogue detections, together with redshift estimates for confirmed clusters, with no duplicate entries. The validation is derived from optical and X-ray follow-up campaigns, supplemented by cross-matching with external catalogues with redshift information, and with XMM-Newton archive data. The external catalogues considered include the all-sky X-ray catalogue MCXC-II, the eROSITA X-ray cluster catalogue, the RASS-MCMF and PSZ-MCMF catalogues, and the extended Planck catalogues of Burenin. A total of 281 clusters are newly-confirmed owing to this process; conversely, 262 Planck candidates are invalidated. Of the 1500 confirmed clusters, 274 have updated redshifts, and 278 have newly-assigned redshifts. An MCXC-II counterpart is assigned to 631 clusters, updating the MCXC cross-match published in the Planck catalogues. Differences with the PSZ2 update of Bahk & Hwang are discussed. We further introduce a new, homogeneously-derived mass estimate, corrected for selection effects owing to intrinsic scatter and the properties of the underlying mass function. New posterior probability contours in the $Y_{5R500}-θ_s$ plane are provided for all sources, in addition to the corresponding $M_{500}(z)$ degeneracy curves. PSZ includes both corrected and uncorrected $M_{500}$ values for confirmed clusters. A methodology for cross-identification between catalogues is presented. We show that simple fixed-distance matching is insufficient for this task, and demonstrate the need for additional consistency checks based on mass proxies, redshifts, and distance versus angular size comparisons. The final PSZ comprises 1500 confirmed clusters, 262 noise-dominated detections, and 200 candidates awaiting validation.

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arXiv2026

Multi-scale weak lensing detection of galaxy clusters with source redshift tomography

Recently, a number of methods have emerged to detect galaxy clusters solely through their weak lensing signal. Using the recently-introduced wavelet multi-scale detection method, we focus here on the potential for the use of tomographic information of the source galaxies to increase the number of weak lensing detections. We apply the $z_{s,\mathrm{min}}$-cut technique, consisting of the combination of weak lensing peak detections emerging from lensing maps obtained using different source redshift bins, to mock data sets of progressively increasing sophistication. The source redshift distribution is chosen to be $Euclid$-like, with a maximum depth of $z_{s,\mathrm{max}}=3$, and overlapping tomographic redshift bins are constructed by progressively increasing the minimum source redshift $z_{s,\mathrm{min}}$. Considering all possible detection combinations from one to four tomographic bins, we find that a single source redshift bin, with $z_{s,\mathrm{min}}=0.4$, performs as well as the combination of multiple redshift bins. By running detections on synthetic clusters of varying complexity -- from isolated Navarro Frenk White haloes to haloes embedded in and formed within N-body cosmological simulations, and considering both true and photometric source redshifts -- we show that while large-scale structure contamination and photometric redshift errors reduce the potential gains of the tomographic approach, the dominant limitation is the accumulation of spurious detections across redshift bins, leading to decreased purity at a fixed detection threshold.

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arXiv2026

CHEX-MATE: Are we getting cluster thermodynamics right?

Galaxy clusters offer powerful insights into the large-scale structure of the Universe and the physics of baryons in hot state. Their scientific exploitation, however, hinges on our ability to accurately measure key thermodynamic properties. In this work, we aim to assess the reliability of current analysis techniques in reconstructing these properties, with particular focus on samples similar to those observed in the Cluster HEritage project with XMM-Newton (CHEX-MATE). We develop a suite of dedicated end-to-end simulations of CHEX-MATE-like clusters selected from large scale hydrodynamical simulations, and processed through a newly developed realistic XMM-Newton simulator. We apply a full X-ray data analysis pipeline to the mock datasets, including imaging, spectral fitting, and profile reconstruction. The gas density profiles can be robustly recovered across a wide radial range, when using azimuthal mean surface brightness profiles. Our reconstruction techniques are able to reproduce the intrinsic density profile with the correct scatter, with deviations of at most 10% between 0.1 and 1xR500c. The gas mass is reconstructed with better than 1% accuracy. Accurate measurement of temperature profiles is more challenging and possibly subject to biases, particularly in the presence of azimuthal variations and multi-temperature gas along the line of sight, which dominate over projection effects. Our results highlight the need for caution in interpreting cluster temperature measurements and underscore the value of tailored mock observations for understanding observational systematics. These findings also suggest that biases in X-ray temperature measurements may alter the interpretation of the thermodynamical state of the intra-cluster medium, an outlook particularly relevant in light of recent low velocity measurements from the XRISM mission.

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arXiv2026

CHEX-MATE: New detections and properties of the radio diffuse emission in massive clusters with MeerKAT

Modern radio telescopes are revolutionising our understanding of non-thermal phenomena in galaxy clusters, collecting large samples of extended sources with unprecedented sensitivity and angular resolution. In this work, we present novel MeerKAT observations for a sample of 21 galaxy clusters that are part of the CHEX-MATE project. These systems were selected based on their high mass and displaying signs of dynamical activity. Thanks to the high-quality data at hand, we were able to detect extended radio emission in every target considered. We report two new halos, one new relic, and two new candidate relics. We also confirm a previous candidate halo and two candidate relics. After investigating the scaling relations with the cluster properties, we confirmed the presence of a radio halo power-mass correlation and relate it to a higher radio halo emissivity in more massive clusters. For radio relics, we highlight the MeerKAT capabilities to significantly extend the depth of radio observations to a new, unexplored field of low-radio power sources ($\lesssim 10^{23} ~ {\rm W~Hz^{-1}} $ at 1.28 GHz). Thanks to such high-sensitivity data, we have found that the radio relic power can be characterised by a wide range of values for a given cluster mass and relic size. Ultimately, we discuss how current radio observations, in combination with large radio surveys, are increasingly capable of testing numerical simulation predictions and coming close to performing direct comparisons with their data, enabling new insights on the evolution of radio relics.

astro-ph.CO↗

arXiv2026

CHEX-MATE: Relationship between X-ray and millimetre inferences of galaxy cluster temperature profiles

Thermodynamic profiles from X-ray and millimetre observations of galaxy clusters are often compared under the simplifying assumptions of smooth, spherically symmetric intracluster medium. These approximations lead to expected discrepancies in the inferred profiles, which can provide insights about the cluster structure or cosmology. Motivated by this, we present a joint XMM-\textit{Newton} and \textit{Planck} analysis of 116 CHEX-MATE clusters to measure $η_T = T_X/T_{SZ,X}$, the ratio between spectroscopic X-ray temperatures and a temperature proxy derived from Sunyaev-Zel'dovich (SZ) pressures and X-ray densities. We considered relativistic corrections to the thermal SZ signal and implemented X-ray absorption by Galactic molecular hydrogen. The $η_T$ distribution has a mean of $1.01 \pm 0.03$, with average changes of $8.1\%$ and $2.7\%$ when relativistic corrections and molecular hydrogen absorption are not included, respectively. The $η_T$ distribution is positively skewed, with the scatter mostly affected by cluster morphology: relaxed clusters are closer to unity and less scattered than mixed and disturbed systems. We find little or no correlation with redshift, mass, or temperature.

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arXiv2025

Thermal Sunyaev-Zel'dovich effect at the core of CL J1226.9+3332 revealed by NOEMA

We present first detailed maps of the thermal Sunyaev-Zel'dovich (tSZ) effect on a $z = 0.89$ cluster with the NOrthern Extended Millimeter Array (NOEMA). The high sensitivity of these observations enabled the effective identification and removal of the millimetre-wave sources contaminating the tSZ signal, thus isolating the influence of the hot electron gas of the cluster on the cosmic microwave background radiation from other emissions. The tSZ observed with success by NOEMA was modelled together with previous single-dish observations (IRAM 30-metre, Green Bank Telescope, and Caltech Sub-millimeter Observatory) to obtain the first core-to-outskirts (from $\sim$ 15 to $\sim$ 1500 kpc) pressure profile reconstruction on such a high-redshift galaxy cluster. NOEMA observations with a high angular resolution have shown that the pressure profile is flat in the core of the cluster. These observations confirm the disturbed nature of CL J1226.9+3332 and map for the first time the distribution of its thermal gas at arcsecond scales in the environments of the central cluster galaxy. Our results showcase the excellent capabilities of NOEMA to complement and enhance the data provided by other millimetre-wave instruments in resolving the core of high-redshift clusters via tSZ emission.

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arXiv2025

CHEX-MATE: towards a consistent universal pressure profile and cluster mass reconstruction

In a self-similar paradigm of structure formation, the thermal pressure of the hot intra-cluster gas follows a universal distribution once the profile of each cluster is normalised based on the proper mass and redshift dependencies. The reconstruction of such a universal pressure profile requires an individual estimate of the mass of each cluster. In this context, we present a method to jointly fit, for the first time, the universal pressure profile and individual cluster $M_{500}$ masses over a sample of galaxy clusters, properly accounting for correlations between the profile shape and amplitude, and masses scaling the individual profiles. We demonstrate the power of the method and show that a consistent exploitation of the universal pressure profile and cluster mass estimates when modelling the thermal pressure in clusters is necessary to avoid biases. In particular, the method, informed by a cluster mass scale, outputs individual cluster masses with same accuracy and better precision than input masses. Using data from the «Cluster HEritage project with XMM-Newton: Mass Assembly and Thermodynamics at the Endpoint of structure formation», we investigate a sample of $\sim 25$ galaxy clusters spanning mass and redshift ranges of $2 \lesssim M_{500}/10^{14} \; \mathrm{M}_{\odot} \lesssim 14$ and $0.07 < z < 0.6$.

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arXiv2025

Implications of SPT and eROSITA cosmologies for Planck cluster number counts and t-SZ power spectrum

Comparison between cosmological studies is usually performed in a statistical manner at the level of the posteriors of cosmological parameters. In this Letter, we show how this approach poorly reflects the differences between cosmological analyses, when applied to cosmological studies using galaxy cluster abundances. We illustrate this by deriving the implications of the best-fit cosmologies from the recent SPT and eROSITA cluster number counts analyses on the Planck thermal Sunyaev-Zeldovich (t-SZ) probes. We first fix the mass calibration, and find that the Planck cluster sample would theoretically contain 498 clusters with the SPT cosmology, and 1098 clusters with the eROSITA cosmology, instead of the 439 clusters observed. We then fit the Planck number counts to both cosmologies, only varying the hydrostatic mass bias, and find required biases of $0.790 \pm 0.070$ and $0.630 \pm 0.034$ for SPT and eROSITA respectively, instead of the $0.844^{+0.055}_{-0.062}$ derived in Aymerich et al. (2025). Lastly, we compute the expected t-SZ power spectrum obtained from the SPT and eROSITA cosmologies, and compare these to the Planck measurement. While the predicted SPT angular power spectrum is in good agreement with the Planck measurements, the normalisation of the predicted eROSITA angular power spectrum is two times higher at all scales. These two tests highlight the power of comparing predicted cluster abundances and t-SZ power spectra to measured data in a physically interpretable way.

astro-ph.CO↗

arXiv2025

Euclid Quick Data Release (Q1). First detections from the galaxy cluster workflow

The first survey data release by the Euclid mission covers approximately $63\,\mathrm{deg^2}$ in the Euclid Deep Fields to the same depth as the Euclid Wide Survey. This paper showcases, for the first time, the performance of cluster finders on Euclid data and presents examples of validated clusters in the Quick Release 1 (Q1) imaging data. We identify clusters using two algorithms (AMICO and PZWav) implemented in the Euclid cluster-detection pipeline. We explore the internal consistency of detections from the two codes, and cross-match detections with known clusters from other surveys using external multi-wavelength and spectroscopic data sets. This enables assessment of the Euclid photometric redshift accuracy and also of systematics such as mis-centring between the optical cluster centre and centres based on X-ray and/or Sunyaev--Zeldovich observations. We report 426 joint PZWav and AMICO-detected clusters with high signal-to-noise ratios over the full Q1 area in the redshift range $0.2 \leq z \leq 1.5$. The chosen redshift and signal-to-noise thresholds are motivated by the photometric quality of the early Euclid data. We provide richness estimates for each of the Euclid-detected clusters and show its correlation with various external cluster mass proxies. Out of the full sample, 77 systems are potentially new to the literature. Overall, the Q1 cluster catalogue demonstrates a successful validation of the workflow ahead of the Euclid Data Release 1, based on the consistency of internal and external properties of Euclid-detected clusters.

astro-ph.CO↗

arXiv2025

Cosmological constraints from the Planck cluster catalogue with DES shear profiles and Chandra observations

We present cosmological constraints from the Planck PSZ2 cosmological cluster sample, using weak-lensing shear profiles from Dark Energy Survey (DES) data and X-ray observations from the Chandra telescope for the mass calibration. We compute hydrostatic mass estimates for all clusters in the PSZ2 sample with a scaling relation between their Sunyaev-Zeldovich signal and X-ray derived hydrostatic mass, calibrated with the Chandra data. We introduce a method to correct these masses with a hydrostatic mass bias using shear profiles from wide-field galaxy surveys. We simultaneously fit the number counts of the PSZ2 sample and the mass calibration with the DES data, finding $Ω_\text{m}=0.312^{+0.018}_{-0.024}$, $σ_8=0.777\pm 0.024$, $S_8\equiv σ_8 \sqrt{Ω_\text{m} / 0.3}=0.791^{+0.023}_{-0.021}$, and $(1-b)=0.844^{+0.055}_{-0.062}$ for our baseline analysis when combined with BAO data. When considering a hydrostatic mass bias evolving with mass, we find $Ω_\text{m}=0.353^{+0.025}_{-0.031}$, $σ_8=0.751\pm 0.023$, and $S_8=0.814^{+0.019}_{-0.020}$. We verify the robustness of our results by exploring a variety of analysis settings, with a particular focus on the definition of the halo centre used for the extraction of shear profiles. We compare our results with a number of other analyses, in particular two recent analyses of cluster samples obtained from SPT and eROSITA data that share the same mass calibration data set. We find that our results are in overall agreement with most late-time probes, in very mild tension with CMB results (1.6$σ$), and in significant tension with results from eROSITA clusters (2.9$σ$). We confirm that our mass calibration is consistent with the eROSITA analysis by comparing masses for clusters present in both Planck and eROSITA samples, eliminating it as a potential cause of tension.

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arXiv2025

NIKA2 Cosmological Legacy Survey: Blind detection of galaxy clusters in the COSMOS field via the Sunyaev-Zel'dovich effect

(Abridged) Clusters of galaxies, formed in the latest stages of structure formation, are unique cosmological probes. With the advent of large CMB surveys like those from the Planck satellite, the ACT and SPT telescopes, we now have access to a large number of galaxy clusters detected at millimeter wavelengths via the thermal Sunyaev-Zel'dovich (tSZ) effect. Nevertheless, it is interesting to complement them with high-angular-resolution (tens of arcseconds) observations to target the lowest-mass and highest-redshift clusters. This is the case of observations with the NIKA2 camera, which is installed on the IRAM 30--m telescope in Pico Veleta, Spain. We used the existing 150 GHz (2 mm) data from the NIKA2 Cosmological Legacy Survey (N2CLS) Large Program to blindly search for galaxy clusters in the well-known COSMOS field, across a 877 arcmin$^2$ region centered on (R.A., Dec.)$_{J2000}$ = (10h00m28.81s, +02d17m30.44s). We first developed a dedicated data reduction pipeline to construct NIKA2 maps at 2 mm. We then used a matched-filter algorithm to extract cluster candidates assuming a universal pressure profile to model the expected cluster tSZ signal. We computed the purity and completeness of the sample by applying the previous algorithm to simulated maps of the sky signal in the COSMOS field. We find a total of 16 cluster candidates at S/N > 4, from which eight have either an optical or X-ray cluster (or group of galaxies) counterpart. This is the first blind detection of clusters of galaxies at mm wavelengths at 18" angular resolution. From this analysis, we confirm that NIKA2 and the IRAM 30--m telescope should be sensitive to low-mass clusters at intermediate and high redshift, complementing current and planned large tSZ-based cluster surveys.

astro-ph.CO↗

arXiv2025

CHEX-MATE: The Impact of Triaxiality and Orientation on Planck SZ Cluster Selection and Weak Lensing Mass Measurements

Galaxy cluster abundance measurements are a valuable tool for constraining cosmological parameters like the mass density ($Ω_m$) and density fluctuation amplitude ($σ_8$). Wide area surveys detect clusters based on observables, such as the total integrated Sunyaev-Zel'dovich effect signal ($Y_{SZ}$) in the case of Planck. Quantifying the survey selection function is necessary for a cosmological analysis, with completeness representing the probability of detecting a cluster as a function of its intrinsic properties. Employing a Monte-Carlo method, we inject triaxial cluster profiles into random positions within the Planck all-sky maps, and subsequently determine the completeness of the Planck-selected CHEXMATE sample as a function of both geometry and SZ brightness. This is then used to generate 1000 mock CHEX-MATE cluster catalogs, and the distribution of shapes and orientations of the detected clusters, along with any associated bias in weak lensing-derived mass ($M_{WL}$) due to this orientation-dependent selection, denoted as $1 - b_χ$, is obtained. We show that cluster orientation impacts completeness, with a higher probability of detecting clusters elongated along the line of sight (LOS). This leads to $1 - b_χ$ values of $0-4\%$ for CHEXMATE clusters relative to a random population. The largest increase in $M_{WL}$ is observed in the lowest mass objects, which are most impacted by orientation-related selection bias. This bias is relevant for upcoming SZ surveys like CMB-S4, and should be considered for surveys utilizing other probes for cluster detection, such as Euclid.

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arXiv2025

A JVLA, GMRT, and XMM study of Abell 795: Large-scale sloshing and a candidate radio phoenix

We present a multiwavelength analysis of the galaxy cluster Abell 795 (z=0.1374), known for its extended (200 kpc) radio emission with a steep spectral index of unclear origin surrounding the brightest cluster galaxy (BCG), and for sloshing features observed by Chandra. We used new JVLA 1.5 GHz, archival GMRT 325 MHz, and XMM-Newton data to investigate the nature of the radio emission and the dynamical state of the intracluster medium. Our X-ray surface brightness analysis revealed an azimuthally asymmetric excess extending to 650 kpc from the center, possibly related to the sloshing spiral, although the existing data did not allow us to confirm the presence of a cold front. We also detected a previously unknown galaxy group located 1 Mpc northwest of the cluster. Its X-ray emission was well fitted by a $β$-model ($β$=0.52$\pm$0.17), and the spectral analysis revealed a thermal plasma temperature kT=1.08$\pm$0.08 keV and metallicity Z=0.13$\pm$0.06 Z$_{\odot}$. We investigated the possibility that this group acted as the perturber that triggered the sloshing in Abell 795, and we showed that the velocity distribution of member galaxies supports the dynamically unrelaxed nature of Abell 795. The analysis of JVLA 1.5 GHz and GMRT 325 MHz images confirmed the presence of extended radio emission with largest linear size 200 kpc, preferentially extended toward southwest and terminating in a sub-component ("SW blob"). We measured the spectral indices, finding $α_{Ext}$=-2.24$\pm$0.13 for the diffuse extended emission, and $α_{SWb}$=-2.10$\pm$0.13 for the SW blob. These ultra-steep spectral index values, coupled with the complex morphology and cospatiality with the radio-loud AGN present in the BCG, suggest that this emission could be classified as a radio phoenix, possibly arising from adiabatic compression of an ancient AGN radio lobe due to the presence of sloshing motions.

astro-ph.GA↗

arXiv2025

CHEX-MATE: Multi-probe analysis of Abell 1689

The nature of the elusive dark matter can be probed by comparing the predictions of the cold dark matter framework with the gravitational field of massive galaxy clusters. However, a robust test of dark matter can only be achieved if the systematic uncertainties in the reconstruction of the gravitational potential are minimized. Techniques based on the properties of intracluster gas rely on the assumption that the gas is in hydrostatic equilibrium within the potential well, whereas gravitational lensing is sensitive to projection effects. Here we attempt to minimize systematics in galaxy cluster mass reconstructions by jointly exploiting the weak gravitational lensing signal and the properties of the hot intracluster gas determined from X-ray and millimeter (Sunyaev-Zel'dovich) observations. We construct a model to fit the multi-probe information within a common framework, accounting for non-thermal pressure support and elongation of the dark matter halo along the line of sight. We then apply our framework to the massive cluster Abell 1689, which features unparalleled multi-wavelength data. In accordance with previous works, we find that the cluster is significantly elongated along the line of sight. Accounting for line-of-sight projections, we require a non-thermal pressure support of $30\text{-}40\%$ at $r_{500}$ to match the gas and weak lensing observables. The joint model retrieves a concentration $c_{200}\sim7$, which is lower and more realistic than the high concentration retrieved from weak lensing data alone under the assumption of spherical symmetry ($c_{200}\sim15$). Application of our method to a larger sample will allow us to study at the same time the shape of dark matter mass profiles and the level of non-thermal pressure support in galaxy clusters.

astro-ph.CO↗