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Observed in a significant fraction of clusters and groups of galaxies, diffuse radio synchrotron emission reveals the presence of relativistic electrons and magnetic fields permeating large scale systems of galaxies. Although, these non-thermal electrons are expected to upscatter cosmic microwave background photons up to hard X-ray energies, such inverse-Compton (IC) X-ray emission has so far not been unambiguously detected on cluster/group scales. Using deep, new proprietary XMM–Newton observations (∼200 ks of clean exposure), we report a 4.6 σ detection of extended IC X-ray emission in MRC 0116 +111, an extraordinary group of galaxies at z = 0.131. Assuming a spectral slope derived from low frequency radio data, the detection remains robust to systematic uncertainties. Together with low frequency radio data from the Giant Metrewave Radio Telescope (GMRT), this detection provides an estimate for the volume-averaged magnetic field of (1.9 ± 0.3) μG within the central part of the group. This value can serve as an anchor for studies of magnetic fields in the largest gravitationally bound systems in the Universe. [ABSTRACT FROM AUTHOR]

In this work, we investigate the dynamical state of the galaxy cluster Abell 2631, a massive structure located at the core of the Saraswati supercluster. To do this, we first solve a tension found in the literature regarding the weak-lensing mass determination of the cluster. We do this through a comprehensive weak-lensing analysis, exploring the power of the combination of shear and magnification data sets. We find |$M_{200}^{\rm wl} = 8.7_{-2.9}^{+2.5} \times 10^{14}$| M⊙. We also determined the mass based on the dynamics of spectroscopic members, corresponding to |$M_{200}^{\rm dy} = 12.2\pm 3.0 \times 10^{14}$| M⊙, consistent within a 68 per cent CL with the weak-lensing estimate. The scenarios provided by the mass distribution and dynamics of galaxies are reconciled with those provided by X-ray observations in a scenario where A2631 is observed at a late stage of merging. [ABSTRACT FROM AUTHOR]

We present the first results of a project called SAGAN, which is dedicated solely to the studies of relatively rare megaparsec-scale radio galaxies in the Universe, called giant radio galaxies (GRGs). We have identified 162 new GRGs primarily from the NRAO VLA Sky Survey with sizes ranging from ∼0.71 Mpc to ∼2.82 Mpc in the redshift range of ∼0.03−0.95, of which 23 are hosted by quasars (giant radio quasars). As part of the project SAGAN, we have created a database of all known GRGs, the GRG catalogue, from the literature (including our new sample); it includes 820 sources. For the first time, we present the multi-wavelength properties of the largest sample of GRGs. This provides new insights into their nature. Our results establish that the distributions of the radio spectral index and the black hole mass of GRGs do not differ from the corresponding distributions of normal-sized radio galaxies (RGs). However, GRGs have a lower Eddington ratio than RGs. Using the mid-infrared data, we classified GRGs in terms of their accretion mode: either a high-power radiatively efficient high-excitation state, or a radiatively inefficient low-excitation state. This enabled us to compare key physical properties of their active galactic nuclei, such as the black hole mass, spin, Eddington ratio, jet kinetic power, total radio power, magnetic field, and size. We find that GRGs in high-excitation state statistically have larger sizes, stronger radio power, jet kinetic power, and higher Eddington ratio than those in low-excitation state. Our analysis reveals a strong correlation between the black hole Eddington ratio and the scaled jet kinetic power, which suggests a disc-jet coupling. Our environmental study reveals that ∼10% of all GRGs may reside at the centres of galaxy clusters, in a denser galactic environment, while the majority appears to reside in a sparse environment. The probability of finding the brightest cluster galaxy as a GRG is quite low and even lower for high-mass clusters. We present new results for GRGs that range from black hole mass to large-scale environment properties. We discuss their formation and growth scenarios, highlighting the key physical factors that cause them to reach their gigantic size. [ABSTRACT FROM AUTHOR]

We present a comprehensive multiwavelength analysis of the merging galaxy cluster MACS J0417.5–1154 at a redshift of |$z$|  = 0.44, using available images red obtained with Chandra in X-ray, Subaru, Hubble Space Telescope (HST) in optical, Giant Metrewave Radio Telescope (GMRT) in radio, and Bolocam at 2.1 mm wavelength. This is an example of a complex merging galaxy cluster also hosting a steep-spectrum Mpc scale radio halo. The mass distribution obtained by weak-lensing reconstruction shows that MACS J0417.5–1154 belongs to the dissociative class of mergers, where one of its substructures has had its gas content detached after the pericentric passage. We find the main cluster mass |$M_{200} = 11.5^{+3.0}_{-3.5} \times 10^{14}\ {\rm M}_\odot$| and the smaller second (sub)cluster mass to be |$M_{200} = 1.96^{+1.60}_{-0.95} \times 10^{14}\ {\rm M}_\odot$|⁠, leading to a large total mass of |$M_{200} = 13.8^{+2.6}_{-2.8} \times 10^{14}\ {\rm M}_\odot$|⁠. The overall structure, surface brightness profile, temperature, and metal abundance of the intracluster medium all point towards the presence of a cold front and merger induced gas-sloshing motion near the core. We detect a surface brightness edge to the southeast direction at a projected distance of ∼45 arcsec (∼255 kpc) from the centre of this cluster. The X-ray spectral analysis across the inner and outer edges allows us to confirm the detected edge as a cold front. The GMRT 235 MHz observation shows a comet-like extended sychrotron radio halo emission trailing behind the cold front. The peak of the Sunyaev–Zel'dovich decrement is found displaced from the centre of X-ray emission, which is interpreted as consequence of the merger dynamics. The optical HST imaging analysis of the cluster reveals the complex morphology of the brightest cluster galaxy, with three surrounding ring-shaped structures with bright knots, which appear to be images of a multiply imaged strongly lensed background galaxy. In addition, two previously unknown giant arcs are found which are all indications of strong gravitational lensing in this massive system. [ABSTRACT FROM AUTHOR]

The galaxy cluster Abell 3376 is a nearby (z = 0.046) dissociative merging cluster surrounded by two prominent radio relics and showing an X-ray comet-like morphology. The merger system is comprised of the subclusters A3376W and A3376E. Based on new deep multiwavelength large-field images and published redshifts, we bring new insights about the history of this merger. Despite the difficulty of applying the weak lensing technique at such low redshift, we successfully recovered the mass distribution in the cluster field. Moreover, with the application of a two-body model, we have addressed the dynamics of this merging system. We have found the individual masses of M200W= 3.0-1.7+1.3 × 1014 M⊚ and M200E= 0.9-0.8+0.5 × 1014 M⊚. The cometary-shaped X-ray distribution shows only one peak spatially coincident with both eastern BCG and the A3376E mass peak whereas the gas content of A3376W seems to be stripped out. Our data allowed us to confirm the existence of a third subcluster located at the north, 1147 ± 62 kpc apart from the neighbour subcluster A3376E and having a mass MN200 = 1.4-1.0+0.7 × 1014 M⊚. From our dynamical analysis, we found the merging is taking place very close to the plane of the sky, with the merger axis just 10° ± 11° from it. The application of a two-body analysis code showed that the merging cluster is seen 0.9-0.3+0.2 Gyr after the pericentric passage and it is currently going to the point of maximum separation between the subclusters. [ABSTRACT FROM AUTHOR]

Context. The cluster Abell 3376 is a merging cluster of galaxies at redshift z = 0.046. It is famous mostly for its giant radio arcs, and shows an elongated and highly substructured X-ray emission, but has not been analysed in detail at optical wavelengths. Aims. To improve our understanding of the effects of the major cluster merger on the galaxy properties, we analyse the galaxy luminosity function (GLF) in the B band in several regions as well as the dynamical properties of the substructures. Methods. We have obtained wide field images of Abell 3376 in the B band and derive the GLF applying a statistical subtraction of the background in three regions: a circle of 0.29 deg radius (1.5 Mpc) encompassing the whole cluster, and two circles centred on each of the two brightest galaxies (BCG2, northeast, coinciding with the peak of X-ray emission, and BCG1, southwest) of radii 0.15 deg (0.775 Mpc). We also compute the GLF in the zone around BCG1, which is covered by the WINGS survey in the B and V bands, by selecting cluster members in the red sequence in a (B - V) versus V diagram. Finally, we discuss the dynamical characteristics of the cluster implied by an analysis based on the Serna & Gerbal (SG) method. Results. The GLFs are not well fit by a single Schechter function, but satisfactory fits are obtained by summing a Gaussian and a Schechter function. The GLF computed by selecting galaxies in the red sequence in the region surrounding BCG1 can also be fit by a Gaussian plus a Schechter function. An excess of galaxies in the brightest bins is detected in the BCG1 and BCG2 regions. The dynamical analysis based on the SG method shows the existence of a main structure of 82 galaxies that can be subdivided into two main substructures of 25 and six galaxies. A smaller structure of six galaxies is also detected. Conclusions. The B band GLFs of Abell 3376 are clearly perturbed, as already found in other merging clusters. The dynamical properties are consistent with the existence of several substructures, which is in agreement with a previously published X-ray analysis. [ABSTRACT FROM AUTHOR]

ABSTRACT We present a multiwavelength study of the energetic interaction between the central active galactic nucleus (AGN), the intracluster medium (ICM) and the optical emission-line nebula in the galaxy cluster Sérsic 159−03. We use X-ray data from Chandra, high-resolution X-ray spectra and ultraviolet (UV) images from XMM-Newton, Hα images from the Southern Astrophysics Research Telescope, Hubble Space Telescope optical imaging, and Very Large Array and Giant Metrewave Radio Telescope radio data. The cluster centre displays signs of powerful AGN feedback, which has cleared the central regions ( r < 7.5 kpc) of a dense, X-ray-emitting ICM. X-ray spectral maps reveal a high-pressure ring surrounding the central AGN at a radius of r∼ 15 kpc, indicating an AGN-driven weak shock. The cluster harbours a bright, 44 kpc long Hα+[N ii] filament extending from the centre of the cD galaxy to the north. Along the filament, we see low-entropy, high-metallicity, cooling X-ray gas. The gas in the filament has most likely been uplifted by 'radio mode' AGN activity and subsequently stripped from the galaxy due to its relative southward motion. Because this X-ray gas has been removed from the direct influence of the AGN jets, part of it cools and forms stars as indicated by the observed dust lanes, molecular and ionized emission-line nebulae and the excess UV emission. [ABSTRACT FROM AUTHOR]