We present new low-frequency ($ν= 88$-216 MHz) observations of the complex merging galaxy cluster Abell 3266. These new observations are taken with the Murchison Widefield Array (MWA) in its Phase II 'extended', long-baseline configuration, offering the highest-resolution low-frequency view of the cluster to date. We report on the detection of four steep spectrum ($α\lesssim -1$ for $S_ν\propto ν^α$) extended radio sources within the cluster. We confirm the detection of a $\sim 570$ kpc radio relic to the south of the cluster, and a possible bridge of emission connecting the relic to the cluster core. We also detect two new ultra-steep-spectrum ($α\lesssim -1.7$) fossil plasma sources to the north and west of the cluster centre without associated compact radio emission. A previously detected radio galaxy in the cluster is also found to have a spectrally steepening tail with steep-spectrum components highlighted by the MWA. We do not detect a giant radio halo in the cluster. After simulating a range of radio haloes at 216 MHz we place upper limits on the radio luminosity corresponding to $\sim 7.2 \times 10^{24}$ W Hz$^{-1}$ at 150 MHz assuming the expected 500 kpc radius, up to a factor 5 lower than expected from scaling relations. Why a giant radio halo is undetected in Abell 3266 is unclear - the timeline of the merger and overall mass of the system as determined by optical and X-ray studies suggest the foundation for a hosting system.
We have selected Abell 3266 to search for ram-pressure induced star formation as a global property of a merging cluster. Abell 3266 (z = 0.0594) is a high mass cluster that features a high velocity dispersion, an infalling subcluster near to the line of sight, and a strong shock front. These phenomena should all contribute to making Abell 3266 an optimum cluster to see the global effects of RPS induced star formation. Using archival X-ray observations and published optical data, we cross-correlate optical spectral properties ([OII, H$β$]), indicative of starburst and post starburst, respective…
Weak lensing and spectroscopic analysis of the nearby dissociative merging galaxy cluster Abell 3376
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 & A3376E. Based on new deep multi-wavelength 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 dyna…
We present the study of the internal dynamics of the intriguing galaxy cluster Abell 1703, a system hosting a probable giant radio halo whose dynamical status is still controversial. Our analysis is based on unpublished spectroscopic data acquired at the Italian Telescopio Nazionale Galileo and data publicly available in the literature. We also use photometric data from the Sloan Digital Sky Survey. We select 147 cluster members and compute the cluster redshift $\left<z\right>\sim 0.277$ and the global line-of-sight velocity dispersion $σ_{\rm v}\sim 1300$ km/s. We infer that Abell 1703 is a m…
Cluster mergers are an important laboratory for studying the behaviour of dark matter (DM) and intracluster gas. There are dissociative collisions that can separate the intracluster gas from the DM. Abell 2034 presents clear dissociative features observed by X-rays and gravitational lensing. The cluster, at $z$ = 0.114, consists of two substructures with mass ratio of about 1:2.2, separated by $\sim$720 kpc. The X-ray emission peak is offcentred from the south DM peak by $\sim$350 kpc. Using N-body hydrodynamical simulations, we aim to reconstruct the dynamic history of the collision, reproduc…
A number of radio observations have revealed the presence of large synchrotron-emitting sources associated with the intra-cluster medium. There is strong observational evidence that the emitting particles have been (re-)accelerated by shocks and turbulence generated during merger events. The particles that are accelerated are thought to have higher initial energies than those in the thermal pool but the origin of such mildly relativistic particles remains uncertain and needs to be further investigated. The galaxy cluster Abell 1914 is a massive galaxy cluster in which X-ray observations show c…
Discovery of a nearby radio relic in the low-mass, merging cluster Abell 4067
University of the Witwatersrand（威特沃特斯兰德大学）；University of Pretoria（比勒陀利亚大学）；SKA Observatory（平方公里阵列射电望远镜天文台）；University of Oxford（牛津大学）；Rhodes University（罗兹大学）；South African Radio Astronomy Observatory（南非射电天文观测站）；Texas A&M University（德克萨斯农工大学）；Chulalongkorn University（朱拉隆功大学）
The pre-merging system of galaxy clusters Abell 3391-Abell 3395 located at a mean redshift of 0.053 has been observed at 1 GHz in an ASKAP/EMU Early Science observation as well as in X-rays with eROSITA. The projected separation of the X-ray peaks of the two clusters is $\sim$50$'$ or $\sim$ 3.1 Mpc. Here we present an inventory of interesting radio sources in this field around this cluster merger. While the eROSITA observations provide clear indications of a bridge of thermal gas between the clusters, neither ASKAP nor MWA observations show any diffuse radio emission coinciding with the X-ray…
Galaxy cluster mergers are a powerful laboratory for testing cosmological and astrophysical models. However, interpreting individual merging clusters depends crucially on their merger configuration, defined by the masses, velocities, impact parameters, and orientation of the merger axis with respect to the plane of the sky. In this work, we investigate the impact of merger parameters on the X-ray emitting intracluster medium and gravitational lensing maps using a suite of idealised simulations of binary cluster mergers performed using the GAMER-2 code. As a test case, we focus on modeling the …
On Dark Peaks and Missing Mass: A Weak Lensing Mass Reconstruction of the Merging Cluster System Abell 520
星系团的合并是独特的，因为它们有能力直接探测和限制暗物质的自相互作用截面。对几个正在合并的星系团的详细观测表明，星系团内的气体会被冲压压力从暗物质和星系密度的质心处移开，而后者的成分在空间上是重合的，这与无碰撞的暗物质是一致的。这被用来确定暗物质粒子自相互作用截面的上限为1 cm ^2/g。星系团Abell 520被认为是一个可能的例外。我们重新审视A520，展示新的HST ACS马赛克图像和麦哲伦图像集。我们进行了详细的弱透镜分析，并表明，弱透镜质量测量和形态的核心星系填充结构大多是在良好的协议与以前的工作。然而，有一个显着的区别-我们没有检测到先前声称的“暗核心”，它包含多余的质量，在X射线等离子体的位置没有显着的星系过密度。这个峰值被认为是暗物质的大的自相互作用截面的指示（至少比子弹星系团观测确定的上限0.7 cm ^2/g大~5 sigma）。我们没有发现这样的迹象，而是发现A520的质量分布，减去X射线等离子体质量后，与星系团星系的光度分布吻合得很好。我们的结论是，A520没有显示出与无碰撞暗物质假设相矛盾的证据。
Abell 3266 is one of the X-ray brightest galaxy clusters in the sky and is a well-known merging system. Using the ability of the eROSITA telescope onboard SRG (Spectrum Röntgen Gamma) to observe a wide field with a single pointing, we analysed a new observation of the cluster out to a radius of R_200. The X-ray images highlight sub-structures present in the cluster, including the north-east--south-west merger seen in previous ASCA, Chandra, and XMM-Newton data, a merging group towards the north-west, and filamentary structures between the core and one or more groups towards the west. We comput…
Revealing the intricacies of radio galaxies and filaments in the merging galaxy cluster Abell 2255. II. Properties of filaments using multi-frequency radio data
Università di Bologna（博洛尼亚大学）；INAF - Istituto di Radioastronomia di Bologna（意大利国家天体物理研究所波洛尼亚射电天文台）；Leiden University（莱顿大学）；ASTRON, The Netherlands Institute for Radio Astronomy（荷兰射电天文研究所）；University of Minnesota（明尼苏达大学）；Universität Hamburg（汉堡大学）；Durham University（杜伦大学）
Context: Chandra observations of the Abell 3411-3412 merging system have revealed an outbound bullet-like sub-cluster in the northern part and many surface brightness (SB) edges at the southern periphery, where multiple diffuse sources are also reported from radio observations. Notably, a south-eastern radio relic associated with fossil plasma from a radio galaxy and with a detected X-ray edge provides direct evidence of shock re-acceleration. The properties of the reported X-ray edges have yet to be constrained from a thermodynamic view. Aims: We use the XMM-Newton and Suzaku observations to …
Revealing the intricacies of radio galaxies and filaments in the merging galaxy cluster Abell 2255. I. Insights from deep LOFAR-VLBI sub-arcsecond resolution images
Diffuse radio emission has been found in many galaxy clusters, predominantly in massive systems which are in the state of merging. The radio emission can usually be classified as relic or halo emission, which are believed to be related to merger shocks or volume-filling turbulence, respectively. Recent observations have revealed radio bridges for some pairs of very closeby galaxy clusters. The mechanisms that may allow to explain the high specific density of relativistic electrons, necessary to explain the radio luminosity of these bridge regions, are poorly explored. We analyse the galaxy clu…
Kelvin-Helmholtz Instabilities (KHI) along contact discontinuities in galaxy clusters have been used to constrain the strength of magnetic fields in galaxy clusters, following the assumption that, as magnetic field lines drape around the interface between the cold and hot phases, their magnetic tension resists the growth of perturbations. This has been observed in simulations of rigid objects moving through magnetised media and sloshing galaxy clusters, and then applied in interpreting observations of merger cold fronts. Using a suite of MHD simulations of binary cluster mergers, we show that …
We present deep ($205 \rm ks$), \Chandra observations of the \ab295 binary merging cluster ($z=0.30$). In the X-ray image, the secondary component is clearly visible as a surface brightness peak, while the primary cluster has a flatter distribution. We found cool gas ($\sim 6 \rm keV$) associated with the secondary, while the central temperature of the primary does not deviate significantly from the mean temperature of the cluster of $\sim 9.5 \rm keV$. In the vicinity of the primary's core we found the hottest region in the cluster accompanied by a surface brightness discontinuity. We propose…
MeerKAT observations of Abell 1775 and Abell 1795: the discovery of a hadronic radio halo?
Leiden University（莱顿大学）；University of Toronto（多伦多大学）；INAF – Istituto di Radioastronomia（意大利国家天体物理研究所射电天文学研究所）；Ruhr-Universität Bochum（波鸿鲁尔大学）；Durham University（杜伦大学）；Università di Bologna（博洛尼亚大学）；University of Hamburg（汉堡大学）
