Synchrotron diffuse emission in merging galaxy clusters and along filaments connecting them demonstrates the presence of relativistic particles and magnetic fields in these environments. The study of the polarized signal associated with this emission represents a powerful tool to constrain the properties of intracluster magnetic fields and the physics of acceleration and transport of relativistic particles. Despite technological progress, detecting this polarized signal is still very challenging. In order to shed light on the capabilities of the SKA telescopes to study this emission, we use the data of cosmological magneto-hydro-dynamic simulations to predict the expected polarized surface brightness of diffuse synchrotron sources from the center of galaxy clusters to filaments of the cosmic web at 1.4 GHz. We explore the possibility to detect these sources with a polarization survey with SKA-Mid with AA4 telescopes and compare the results with those from pointed observations corresponding to longer exposure times. These simulations provide precious information to understand the potential of the SKA telescopes for studying the origin and evolution of cosmological magnetic fields. We discuss how these observations can be used in order to characterize the magnetic field and the distribution and energy content of the radio emitting plasma and to shed light on the link between non-thermal and thermal properties and the dynamical state of the system.

Aims. Understanding the origin and evolution of cosmological magnetic fields requires a detailed knowledge of the strength of magnetic fields in different extragalactic environments. In this context, a powerful tool is the statistical analysis of the Faraday effect on the linear polarization of a sample of radio sources. This effect carries information about the magnetic fields in our Galaxy, in extragalactic environments between the sources and the observer, and within the emitting radio source itself. An accurate disentangling of all these components is crucial in order to characterize magnetic fields in the large-scale structure of the Universe. Methods. The significant amount of data delivered by new radio instruments enables the investigation of increasingly weak magnetic fields. However, a trustworthy characterization is only possible with advanced analysis techniques. In this work, we present a new algorithm capable of simultaneously disentangling the Faraday effect due to our Galaxy from extragalactic contributions, by properly taking into account the observing noise. The algorithm takes as input a catalogue of Faraday depth measurements complemented by auxiliary information, for example as the redshift of the sources. Results. We tested the algorithm with synthetic data to assess its performance and to identify the range of slopes of the Galactic magnetic field power spectrum that allows us to properly disentangle Galactic and extragalactic contributions. Furthermore, we tested the algorithm with synthetic catalogues, based on metre and centimetre data currently available, corresponding to different observing set-ups, noise, and cuts in the absolute value of the Galactic latitude of the radio sources. Considering noise values and density of polarized sources consistent with existing catalogues, we demonstrated that the most robust results are obtained with sources with absolute Galactic latitude greater than 45 degrees, with inference of the extragalactic parameters at most within 5σ, both for dispersion in Faraday rotation of about 1 and 10 rad/m2.

Understanding cosmological magnetic fields requires a detailed knowledge of magnetism in the different environments of the large-scale structure of the Universe. Magnetic fields are well known to inhabit galaxy clusters, and recently their presence has been detected between galaxy clusters, along filaments extending up to 10-15 Mpc. Beyond that, there is limited information on the existence of magnetic fields in sheets and voids of the cosmic web. We propose a Bayesian statistical approach to study magnetic fields on large scales through observations of the Faraday rotation effect in large samples of polarized point-like background radio sources. We present the expectations to detect magnetization in environments of the large-scale structure with the SKA-Mid polarization survey planned by the SKAO Magnetism Science Working Group and with SKA-Low with AA4 telescopes, and discuss the required level of accuracy on the redshifts of the host galaxies for such a study. We find that about 50,000 mid-frequency Faraday rotation measurements complemented by high-precision redshifts are needed to constrain magnetization of dense environments as galaxy clusters. Investigation of magnetization in weakly-magnetized low-density enviroments, as filaments, will remain challenging, but low frequencies radio observations and spectroscopic redhifts for at least 17,000 will allow us to put first constraints.

Large-scale magnetic fields in galaxy clusters can influence their physics and the evolution of cluster-embedded galaxies. These properties remain poorly constrained due to a historical lack of high-sensitivity and high-resolution spectropolarimetric data. Thanks to the advent of the Square Kilometre Array pathfinders and precursors, this situation is now dramatically changing. Using the densest rotation measure (RM) grid produced to date from broadband spectropolarimetric data within the MeerKAT Fornax Survey (508 sources over 6.35 deg(2); presented in a previous paper), we aim to study the Fornax cluster's magnetic field in detail. We compared the RM grid properties with numerical simulations to constrain the strength and the structure of the intracluster magnetic field. We modelled the magnetic field power spectrum with a power law, and find a slope of 2.7(-0.4)(+0.2), fluctuating between minimum and a maximum scales of 1.01(-0.02)(+0.01) and 15(-2)(+9) kpc, respectively. It has a central strength of 5.0(-0.4)(+0.3) mu G, decreasing with the thermal plasma density according to a power-law exponent eta = 1.6(-0.5)(+0.3), the highest value to date in large-scale systems. By analysing a sample of 17 galaxy clusters and groups with magnetic field estimates from the literature, we observe longer autocorrelation lengths in the case of massive merging clusters and lower values for relaxed clusters and low-mass clusters or galaxy groups. We also observe a systematic increase in the central magnetic field strength as a function of central density, B-0 proportional to n(0)((0.38 +/- 0.14)). We argue that the steepening of the Fornax cluster's magnetic field profile and its relatively high central strength could indicate a recent re-amplification at the centre due to the extended central radio galaxy. The sample analysis supports the proposed scenario; however, more detailed magnetic field studies conducted using consistent modelling on larger samples are needed to better understand magnetisation in clusters and groups.

The presence of diffuse radio sources in galaxy clusters and the recent discovery of polarized signals associated with the tails of a jellyfish galaxy indicates that intra-cluster/intra-group magnetic fields can influence the physics of these environments and the evolution of the embedded galaxies. A better reconstruction of the properties of such fields is therefore fundamental to understand in detail the physical processes in galaxy groups and clusters and the evolution of the embedded sources. The SKAO represents a great opportunity to perform these studies through the analysis of the so-called rotation measure (RM) grid, since polarization properties of radio sources are modified by the intervening magnetic field. In this manuscript, we illustrate the prediction on the density of the RM grid considering the SKA-mid polarization survey planned by the SKA Magnetism Science Working Group. Moreover, we describe how it is possible to measure intra-cluster/intra-group magnetic fields with the RM grid. Eventually, we quantify the improvement in the precision and accuracy of the magnetic field measurements compared to what is achievable with current surveys such as the POSSUM survey.

Using the Square Kilometre Array (SKA) mid precursor MeerKAT, we acquired broadband spectro-polarimetric data in the context of the MeerKAT Fornax Survey to study the Fornax cluster’s magnetic fields in detail by building the densest rotation measure (RM) grid to date. Here, we present the survey, the analysis, and a discussion of the RM grid properties. We analyzed a circular region centered on the Fornax cluster center with a radius of ∼1.4°; that is, ∼0.73 R vir . The mosaics have a resolution of 13″ and cover the frequencies between 900 MHz and 1.4 GHz, reaching an average noise of 16 μJy beam −1 in total intensity and 3 μJy beam −1 in the Q and U Stokes images. With these data, we detected 508 polarized sources over an area of ∼6.35 deg 2 corresponding to a density of ∼80 polarized sources/deg 2 . This is the densest RM grid ever built. Of the polarized sources, five are cluster sources. Excluding the cluster sources, we built the Euclidean-normalized differential source counts in polarization and we went a factor of ten deeper than previous surveys. We tentatively detect for the first time an increment in the differential source counts at low polarized flux densities; that is, ∼9 μJy at 1.4 GHz. The average degree of polarization of about 3–4% suggests that the sub-μJansky population is not dominated by star-forming galaxies, typically showing a degree of polarization lower than 1%. The majority of the polarized sources are Faraday simple; in other words, their polarization plane rotates linearly with the wavelength squared. The RM shows the typical decrement going from the center to the outskirts of the Fornax cluster. However, interesting features are observed both in the RM grid and in the RM radial profiles across different directions. A combination of the cluster physics and large-scale structure filaments surrounding the Fornax cluster could explain the RM characteristics.

We present TUNA, a Vision-Transformer based network adapted from segmentation to flux regression for faint, diffuse radio emission. Trained on LOFAR-like mock observations derived from cosmological simulations, TUNA accurately reconstructs low surface-brightness structures, with only mild smoothing and small brightness-dependent biases. Applied to LOFAR data of the A399 - A401 galaxy cluster system, it recovers the ridge not identifiable in the high resolution observation and matches the low resolution tapered map. These results indicate how TUNA can deliver automated, quantitative surface brightness estimates for diffuse extragalactic sources, enabling scalable analyses for upcoming surveys.

We describe the design and performance of the cryostat and the multi-stage sub-K single-shot sorption cooler for the MIllimeter Sardinia Radio Telescope Receiver based on Array of Lumped elements kids (MISTRAL) experiment. MISTRAL is a W-band (77 - 103 GHz) Ti/Al bi-layer Lumped Elements Kinetic Inductance Detectors (LEKIDs) camera working at the Gregorian focus of the 64 m aperture Sardinia Radio Telescope (SRT), located in Sardinia (Italy). The cryogenic system, based on a 1.5 W at 4.2 K Pulse Tube (PT) cryocooler, provides the 4 K base temperature for the sub-K refrigerator, and cools down the cold optics and the filters chain of the instrument. The sub-K sorption cooler consists of two intermediate stages, ^4 He and ^3 He sorption refrigerators that allow to reduce the heat load on the ultra-cold head, and a twin stage of ^3 He sorption refrigerator providing the 0.2 K operation temperature for the 415-pixel array of LEKIDs. MISTRAL experiment was installed at SRT in May 2023, the technical commissioning started in June 2023. We will show the performance of the system in the laboratory.

Vision Transformers are used via a customized TransUNet architecture, which is a hybrid model combining Transformers into a U-Net backbone, to achieve precise, automated, and fast segmentation of radio astronomy data affected by calibration and imaging artifacts, addressing the identification of faint, diffuse radio sources. Trained on mock radio observations from numerical simulations, the network is applied to the LOFAR Two-meter Sky Survey data. It is then evaluated on key use cases, specifically megahalos and bridges between galaxy clusters, to assess its performance in targeting sources at different resolutions and at the sensitivity limits of the telescope. The network is capable of detecting low surface brightness radio emission without manual source subtraction or re-imaging. The results demonstrate its groundbreaking capability to identify sources that typically require reprocessing at resolutions 4-6 times lower than that of the input image, accurately capturing their morphology and ensuring detection completeness. This approach represents a significant advancement in accelerating discovery within the large datasets generated by next-generation radio telescopes.

Galaxy clusters and surrounding medium, can be studied using X-ray bremsstrahlung emission and Sunyaev Zel’dovich (SZ) effect. Both astrophysical probes, sample the same environment with different parameters dependance. The SZ effect is relatively more sensitive in low density environments and thus is useful to study the filamentary structures of the cosmic web. In addition, observations of the matter distribution require high angular resolution in order to be able to map the matter distribution within and around galaxy clusters. MISTRAL is a camera working at 90GHz which, once coupled to the Sardinia Radio Telescope (SRT), can reach 12″ angular resolution over 4′ field of view (f.o.v.). The forecasted sensitivity drives to a Noise Equivalent Flux Density of ≃ 10–15 mJy √s and the mapping speed is MS = 380′2 mJy−2 h−1. MISTRAL was recently installed at the focus of the SRT and soon will take its first photons.

The MIllimeter Sardinia radio Telescope Receiver based on Array of Lumped elements KIDs, MISTRAL, is a cryogenic LEKID camera, operating in the W band ( 77-103 GHz ) from the Gregorian focus of the 64-m aperture Sardinia Radio Telescope (SRT), in Italy. This instrument features a high angular resolution ( ∼12 arcsec ) and a wide instantaneous field of view ( ∼4 arcmin ), allowing continuum surveys of the mm-wave sky with many scientific targets, including observations of galaxy clusters via the Sunyaev–Zel’dovich effect. In May 2023, MISTRAL has been installed at SRT for the technical commissioning. In this contribution, we will describe the MISTRAL instrument focusing on the laboratory characterization of its focal plane: a ∼400 -pixel LEKID array. We will show the optical performance of the detectors highlighting the procedure for the identification of the pixels on the focal plane, the measurements of the optical responsivity and NEP, and the estimation of the optical efficiency.

The relation between giant radio halos and mini-halos in galaxy clusters is not understood. The former are usually associated with merging clusters, the latter are found in relaxed systems. In the last years, the advent of low-frequency radio observations has challenged this dichotomy, finding intermediate objects with a hybrid radio morphology. We aim to investigate the presence of diffuse radio emission in the cluster Abell 1413 and determine its dynamical status. We used LOFAR HBA observations centred at 144 MHz to study the diffuse emission hosted by this cluster.To investigate the dynamical state of the system, we complete our study with newly analysed XMM-Newton archival data. A1413 shows features that are typically present in both relaxed (e.g., peaked x-ray surface brightness distribution and little large-scale inhomogeneities) and disturbed (e.g., flatter temperature and metallicity profiles) clusters.This evidence supports the scenario that A1413 is neither a disturbed nor fully relaxed object. We argue that it is an intermediate-phase cluster.Using radio observations at 144 MHz, we discover the presence of a wider diffuse component surrounding the previously reported mini-halo at the cluster centre. By fitting the radio surface brightness profile with a double-exponential model, we can disentangle the two components. We find an inner mini-halo with an e-folding radius r_e1=28 kpc and the extended component with r_e2 = 290 kpc. We also performed point-to-point correlations between radio and X-ray surface brightness, finding a sub-linear relation for the outer emission and a super-linear relation for the mini-halo.The mini-halo and the diffuse emission extend over different scales and show different features, confirming the double nature of the radio emission and suggesting that the mechanisms responsible for the re-acceleration of the radio-emitting particle might be different.

This paper describes the design and performance of the single-pixel receiver elements in the Cryogenic Array Receiver for Users of the Sardinia Observatory (CARUSO). CARUSO contains an array of 4x4 extended-W-band pixels, covering astronomical source frequencies from 70 to 116 GHz. CARUSO has recently been installed at the Gregorian focus of the 64 m diameter Sardinia Radio Telescope. Each cryogenic receiver pixel comprises a smooth walled feedhorn and a waveguide orthomode transducer for polarization separation. Each polarization channel comprises two low-noise amplification modules with a waveguide isolator between them, and an image-rejecting sub-harmonic mixer delivering the upper and lower sidebands, with a frequency tripler providing the local oscillator signal. The low noise amplifiers are based on two-stage MMIC amplifiers, incorporating InP high electron mobility transistors.

We present deep total intensity and polarization observations of the Coma cluster at 1.4 and 6.6 GHz performed with the Sardinia Radio Telescope. By combining the single-dish 1.4 GHz data with archival Very Large Array observations, we obtain new images of the central radio halo and of the peripheral radio relic where we properly recover the brightness from the large-scale structures. At 6.6 GHz, we detect both the relic and the central part of the halo in total intensity and polarization. These are the highest frequency images available to date for these radio sources in this galaxy cluster. In the halo, we find a localized spot of polarized signal, with fractional polarization of about 45 per cent. The polarized emission possibly extends along the north-east side of the diffuse emission. The relic is highly polarized, up to 55 per cent, as usually found for these sources. We confirm the halo spectrum is curved, in agreement with previous single-dish results. The spectral index is alpha = 1.48 +/- 0.07 at a reference frequency of 1 GHz and varies from alpha similar or equal to 1.1, at 0.1 GHz, up to alpha similar or equal to 1.8, at 10 GHz. We compare the Coma radio halo surface brightness profile at 1.4 GHz (central brightness and e-folding radius) with the same properties of the other haloes, and we find that it has one of the lowest emissivities observed so far. Reanalysing the relic's spectrum in the light of the new data, we obtain a refined radio Mach number of M = 2.9 +/- 0.1.

We present the results of observations performed with the Sardinia Radio Telescope (SRT) at 1.3-1.8 GHz of the galaxy cluster CL 0217 + 70 and a 3 degrees x 3 degrees region around it. We combine the SRT data with archival Very Large Array (VLA) data to obtain images having the VLA angular resolution, but sensitive up to largest scales. The SRT + VLA combination allows us to derive a cluster radio halo flux density higher by similar to 14per cent compared to the VLA-only data, although consistent within 1 sigma. We derive a spectral index map between 140 MHz and 1.4 GHz, finding an extended region with spectral index alpha similar to 0.6 on the external part of the south-eastern candidate relic, questioning the real nature of this relic. Moreover, we detect an extended emission outside the cluster in the south-eastern area, having an angular extension of similar to 50 arcmin on the longer side, which would correspond to similar to 10 Mpc at the cluster distance; the emissivity that this region would have if located at the cluster distance is in line with the one estimated in candidate filaments of the cosmic web; however, the peculiar orientation of this region, not pointed towards the cluster, and the low Galactic latitude of this cluster suggest that its origin can be due to a foreground emission originating in our Galaxy.

The Millimeter Sardinia radio Telescope Receiver based on Array of Lumped elements KIDs (MISTRAL) is a new high resolution, wide field-of-view camera that was successfully installed in May 2023 at the Sardinia Radio Telescope (SRT). SRT is a 64 m fully steerable gregorian radio telescope, and it underwent an upgrade funded by a National Operational Program (PON) with the aim to expand the fleet of receivers of the radio telescope in order to cover frequency up to the W-band. The W-band sky has been extensively studied by Cosmic Microwave Background experiments, both ground-based (ACT, SPT) and satellite-based (WMAP, Planck). However, their resolution is limited to approximate to 1 '' from ground telescopes and approximate to 10 ' from satellite at best. With this new instrument, we aim to map the microwave sky at a resolution of approximate to 12 '', a capability only shared by few instruments in the world, unlocking the exploration of a plethora of science cases from the recently upgraded SRT. The heart of MISTRAL is a approximate to 90 mm silicon focal plane populated with 415 cryogenic Lumped Elements Kinetic Inductance Detectors (LEKIDs). These detectors are copuled with the telescope using a cold (4K) re-imaging optical system, producing a diffraction limited field-of-view of 4 '. The system is enclosed in a custom, four stage cryostat, built with strict requirements on its size, in order to fit on the rotating turret that allows to switch the receivers to be quickly moved in and out of the gregorian focus position. The sub-K stage cools the detectors down to 200-240 mK. MISTRAL is now installed on the gregorian focus of SRT and is undergoing the technical commissioning, and will soon enter the scientific commissioning phase. In this contribution we will survey the subsystems of MISTRAL and their performance at the focus of the radio telescope, and report the current status of the technical commissioning.