Understanding the radio relic emission in the galaxy cluster MACS J0717.5+3745: spectral analysis
K. Rajpurohit, D. Wittor, R. J. van Weeren, F. Vazza, M. Hoeft, L. Rudnick, N. Locatelli, J. Eilek, W. R. Forman, A. Bonafede, E. Bonnassieux, C. J. Riseley, M.… 展开作者
K. Rajpurohit, D. Wittor, R. J. van Weeren, F. Vazza, M. Hoeft, L. Rudnick, N. Locatelli, J. Eilek, W. R. Forman, A. Bonafede, E. Bonnassieux, C. J. Riseley, M. Brienza, G. Brunetti, M. Brüggen, F. Loi, A. S. Rajpurohit, H. J. A. Röttgering, A. Botteon, T. E. Clarke, A. Drabent, P. Domínguez-Fernández, G. Di Gennaro, F. Gastaldello
Radio relics are diffuse, extended synchrotron sources that originate from shock fronts generated during cluster mergers. The massive merging galaxy cluster MACS J0717.5+3745 hosts one of the more complex relics known to date. We present upgraded Giant Metrewave Radio Telescope band 3 (300-500 MHz) and band 4 (550-850 MHz) observations. These new observations, combined with published VLA and the new LOFAR HBA data, allow us to carry out a detailed, high spatial resolution spectral analysis of the relic over a broad range of frequencies. The integrated spectrum of the relic closely follows a power-law between 144 MHz and 5.5 GHz with a mean spectral slope $α=-1.16\pm0.03$. Despite its complex morphology, the subregions of the relic and the other isolated filaments also follow power-law behaviors, and show similar spectral slopes. Assuming Diffusive Shock Acceleration, we estimate a dominant Mach number of $\sim 3.7$ for the shocks that make up the relic. Comparison with recent numerical simulations suggests that in the case of radio relics, the slopes of the integrated radio spectra are determined by the Mach number of the accelerating shock, with $α$ nearly constant, namely between $-1.13$ and $-1.17$, for Mach numbers $3.5 - 4.0$. The spectral shapes inferred from spatially resolved regions show curvature, we speculate that the relic is inclined along the line-of-sight. The locus of points in the simulated color-color plots changes significantly with the relic viewing angle. We conclude that projection effects and inhomogeneities in the shock Mach number dominate the observed spectral properties of the relic in this complex system. Based on the new observations we raise the possibility that the relic and a narrow-angle-tailed radio galaxy are two different structures projected along the same line-of-sight.
We report the discovery of a radio halo in the massive merging cluster MACSJ2243.3-0935, as well as a new radio relic candidate, using the Giant Meterwave Radio Telescope and the KAT-7 telescope. The radio halo is coincident with the cluster X-ray emission and has a largest linear scale of approximately 0.9 Mpc. We measure a flux density of $10.0\pm 2.0$ mJy at 610 MHz for the radio halo. We discuss equipartition estimates of the cluster magnetic field and constrain the value to be of the order of 1 $μ$G. The relic candidate is detected at the cluster virial radius where a filament meets the c…
Galaxy-cluster merger shocks efficiently accelerate the ambient electrons through diffusive shock acceleration and amplify magnetic field by compressing the Inter Cluster Medium. As a result, such objects produce a significant amount of synchrotron radio emission. Radio halo and Mpc scale peripheral radio relics thus help us to trace back the cluster formation history. To study the dynamical state of the galaxy clusters and their relation to the merging scenario, as a pilot project, we thus observed four suitable candidates from the MACS (Massive Cluster Survey) cluster sample. Observations we…
We present a strong-lensing analysis of four massive galaxy clusters imaged with the Hubble Space Telescope in the Reionization Lensing Cluster Survey. We use a Light-Traces-Mass technique to uncover sets of multiply images and constrain the mass distribution of the clusters. These mass models are the first published for Abell S295 and MACS J0159.8-0849, and are improvements over previous models for Abell 697 and MACS J0025.4-1222. Our analysis for MACS J0025.4-1222 and Abell S295 shows a bimodal mass distribution supporting the merger scenarios proposed for these clusters. The updated model f…
The investigation of merging galaxy clusters that exhibit radio relics is strengthening our understanding of the formation and evolution of galaxy clusters, the nature of dark matter, the intracluster medium, and astrophysical particle acceleration. Each merging cluster provides only a single view of the cluster formation process and the variety of merging clusters is vast. Clusters hosting double radio relics are rare and extremely important because they allow tight constraints on the merger scenario. We present a weak-lensing and X-ray analysis of MACSJ1752.0+4440 ($z$=0.365) and ZWCL1856.8+…
Mergers of galaxy clusters are among the most energetic events in the Universe. These events have significant impact on the intra-cluster medium, depositing vast amounts of energy - often in the form of shocks - as well as heavily influencing the properties of the constituent galaxy population. Many clusters have been shown to host large-scale diffuse radio emission, known variously as radio haloes and relics. These sources arise as a result of electron (re-)acceleration in cluster-scale magnetic fields, although the processes by which this occurs are still poorly understood. We present new, d…
Merging galaxy clusters produce low Mach number shocks in the intracluster medium. These shocks can accelerate electrons to relativistic energies that are detectable at radio frequencies. MACS J0744.9+3927 is a massive ($M_{500} = (11.8 \pm 2.8) \times 10^{14} M_{\odot}$), high-redshift ($z=0.6976$) cluster where a Bullet-type merger is presumed to have taken place. Sunyaev-Zel'dovich maps from MUSTANG indicate that a shock, with Mach number $\mathcal{M} = 1.0-2.9$ and an extension of $\sim 200$ kpc, sits near the centre of the cluster. The shock is also detected as a brightness and temperatur…
To investigate the relationship between thermal and non-thermal components in merger galaxy clusters, we present deep JVLA and Chandra observations of the HST Frontier Fields cluster MACS J0717.5+3745. The Chandra image shows a complex merger event, with at least four components belonging to different merging subclusters. NW of the cluster, $\sim 0.7$ Mpc from the center, there is a ram-pressure-stripped core that appears to have traversed the densest parts of the cluster after entering the ICM from the direction of a galaxy filament to the SE. We detect a density discontinuity NNE of this cor…
Strong gravitational lensing by clusters of galaxies probes the mass distribution at the core of each cluster and magnifies the universe behind it. MACS J0417.5-1154 at z=0.443 is one of the most massive clusters known based on weak lensing, X-ray, and Sunyaev-Zel'dovich analyses. Here we compute a strong lens model of MACS J0417 based on Hubble Space Telescope imaging observations collected, in part, by the Reionization Lensing Cluster Survey (RELICS), and recently reported spectroscopic redshifts from the MUSE instrument on the Very Large Telescope (VLT). We measure an Einstein radius of The…
In this paper we present results from a radio-optical study of the galaxy populations of the galaxy clusters Abell 1300 and MACS J1931.8$-$2634, a merger and a relaxed system respectively both located at $z \sim 0.3$, aimed at finding evidence of merger-induced radio emission. Radio observations are taken at 1.28 GHz with the MeerKAT interferometer during its early-stage commissioning phase, and combined with archive optical data. We generated catalogues containing 107 and 162 radio sources in the A$~$1300 and MACS J1931.8--2634 cluster fields respectively, above a 0.2 mJy threshold and within…
We report the discovery of large-scale diffuse radio emission South-East of the galaxy cluster MACS J0520.7-1328, detected through high sensitivity Giant Metrewave Radio Telescope 323 MHz observations. This emission is dominated by an elongated diffuse radio source and surrounded by other features of lower surface brightness. Patches of these faint sources are marginally detected in a 1.4 GHz image obtained through a re-analysis of archival NVSS data. Interestingly, the elongated radio source coincides with a previously unclassified extended X-ray source. We perform a multi-wavelength analysis…
The goal of the present study is to extend our current knowledge of the diffuse radio source (halo and relic) populations to $z$ $>$ 0.3. Here we report GMRT and EVLA radio observations of six galaxy clusters taken from the MAssive Cluster Survey (MACS) catalogue to detect diffuse radio emission. We used archival GMRT (150, 235 and 610 MHz) and EVLA (L band) data and made images at multiple radio frequencies of the following six clusters - MACSJ0417.5-1154, MACSJ1131.8-1955, MACSJ0308.9+2645, MACSJ2243.3-0935, MACSJ2228.5+2036 and MACSJ0358.8-2955. We detect diffuse radio emission (halo or rel…
We report on high-resolution JVLA and Chandra observations of the HST Frontier Cluster MACS J0717.5+3745. MACS J0717.5+3745 offers the largest contiguous magnified area of any known cluster, making it a promising target to search for lensed radio and X-ray sources. With the high-resolution 1.0-6.5 GHz JVLA imaging in A and B configuration, we detect a total of 51 compact radio sources within the area covered by the HST imaging. Within this sample we find 7 lensed sources with amplification factors larger than $2$. None of these sources are identified as multiply-lensed. Based on the radio lumi…
We present a comprehensive multi-wavelength 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, {\it Subaru}, {\it Hubble Space Telescope} (HST) in optical, {\it Giant Metrewave Radio Telescope} (GMRT) in radio and {\it 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…
We investigate the possible presence of diffuse radio emission in the intermediate redshift, massive cluster PLCK G285.0-23.7 (z=0.39, M_500 = 8.39 x 10^(14) M_Sun). Our 16cm-band ATCA observations of PLCK G285.0-23.7 allow us to reach a rms noise level of ~11 microJy/beam on the wide-band (1.1-3.1 GHz), full-resolution (~5 arcsec) image of the cluster, making it one of the deepest ATCA images yet published. We also re-image visibilities at lower resolution in order to achieve a better sensitivity to low-surface-brightness extended radio sources. We detect one of the lowest luminosity radio ha…
We present 5.5 and 9.0 GHz Australia Telescope Compact Array (ATCA) observations of the cluster MACSJ0417.5-1154, one of the most massive galaxy clusters and one of the brightest in X-ray in the Massive Cluster Survey (MACS). We estimate diffuse emission at 5.5 and 9.0 GHz from our ATCA observations, and compare the results with the 235 MHz and 610 MHz GMRT observations and 1575 MHz VLA observations. We also estimate the diffuse emission at low frequencies from existing GLEAM survey data (using the MWA telescope), and find that the steepening reported in earlier studies may have been an artefa…
A fraction of galaxy clusters host diffuse radio sources whose origins are investigated through multi-wavelength studies of cluster samples. We investigate the presence of diffuse radio emission in a sample of seven galaxy clusters in the largely unexplored intermediate redshift range (0.3 < z < 0.44). In search of diffuse emission, deep radio imaging of the clusters are presented from wide band (1.1-3.1 GHz), full resolution ($\sim$ 5 arcsec) observations with the Australia Telescope Compact Array (ATCA). The visibilities were also imaged at lower resolution after point source modelling and s…
The Frontier Fields project is an observational campaign targeting six galaxy clusters, with the intention of using the magnification provided by gravitational lensing to study galaxies that are extremely faint or distant. We used the Karl G. Jansky Very Large Array (VLA) at 3 and 6 GHz to observe three Frontier Fields: MACSJ0416.1$-$2403 ($z$ = 0.396), MACSJ0717.5+3745 ($z$ = 0.545), and MACSJ1149.5+2223 ($z$ = 0.543). The images reach noise levels of $\sim$1 $μ$Jy beam$^{-1}$ with sub-arcsecond resolution ($\sim$2.5 kpc at $z$ = 3), providing a high-resolution view of high-$z$ star-forming g…
The diffusive shock acceleration scenario is usually invoked to explain radio relics, although the detailed driving mechanism is still a matter of debate. Our aim is to constrain models for the origin of radio relics by comparing observed relic samples with simulated ones. Here we present a framework to homogeneously extract the whole sample of known radio relics from NVSS so that it can be used for comparison with cosmological simulations. In this way, we can better handle intrinsic biases in the analysis of the radio relic population. In addition, we show some properties of the resulting NVS…
We present new LOFAR observations of the massive merging galaxy cluster MACS J0717.5+3745. The cluster hosts the most powerful radio halo known to date. These new observations, in combination with published uGMRT (300$-$850 MHz) and VLA (1$-$6.5 GHz) data, reveal that the halo is more extended than previously thought, with a largest linear size of $\sim2.2 \rm Mpc$. The halo shows a steep spectrum ($α_{144\,\text{MHz}}^{1.5\,\text{GHz}}\sim-1.4$) and a steepening ($α_{1.5 \text{GHz}}^{5.5 \text{GHz}}\sim-1.9$) above 1.5 GHz. We find a strong scattering in spectral index maps on scales of 50$-$…
We present results from LOFAR and GMRT observations of the galaxy cluster MACS$\,$J0717.5$+$3745. The cluster is undergoing a violent merger involving at least four sub-clusters, and it is known to host a radio halo. LOFAR observations reveal new sources of radio emission in the Intra-Cluster Medium: (i) a radio bridge that connects the cluster to a head-tail radio galaxy located along a filament of galaxies falling into the main cluster, (ii) a 1.9 Mpc radio arc, that is located North West of the main mass component, (iii) radio emission along the X-ray bar, that traces the gas in the X-rays …
Radio emission in the form of giant radio relics is observed at the periphery of galaxy clusters. This non-thermal emission is an important tracer for cosmic-ray electrons and intracluster magnetic fields. One striking observational feature of these objects is their high degree of polarisation which provides information on the magnetic fields at the relics' positions. In this contribution, we test if state-of-the-art high resolution cosmological simulations are able to reproduce the polarisation features of radio relics. Therefore, we present a new analysis of high-resolution cosmological simu…
The HST Frontier Fields cluster MACS J1149.6+2223 is one of the most complex merging clusters, believed to consist of four dark matter halos. We present results from deep (365 ks) Chandra observations of the cluster, which reveal the most distant cold front (z=0.544) discovered to date. In the cluster outskirts, we also detect hints of a surface brightness edge that could be the bow shock preceding the cold front. The substructure analysis of the cluster identified several components with large relative radial velocities, thus indicating that at least some collisions occur almost along the lin…
Radio relics in galaxy clusters are believed to trace merger shock fronts. If cosmological structure formation determines the luminosity, size and shape distributions of radio relics then merger shocks need to be lighted up in a homogeneous way. We investigate if a mock relic sample, obtained from zoomed galaxy cluster simulations, is able to match the properties of relics measured in the NRAO VLA Sky Survey (NVSS). We compile a list of all radio relics known to date and homogeneously measure their parameters in all NVSS images and apply the same procedure to relics in our simulations. Number …
Merging galaxy clusters leave long-lasting signatures on the baryonic and non-baryonic cluster constituents, including shock fronts, cold fronts, X-ray substructure, radio halos, and offsets between the dark matter and the gas components. Using observations from Chandra, the Jansky Very Large Array, the Giant Metrewave Radio Telescope, and the Hubble Space Telescope, we present a multiwavelength analysis of the merging Frontier Fields cluster MACS J0416.1-2403 (z=0.396), which consists of a NE and a SW subclusters whose cores are separated on the sky by ~250 kpc. We find that the NE subcluster…
The galaxy cluster ZwCl 2341.1+0000 is a merging system at z=0.27, which hosts two radio relics and a central, faint, filamentary radio structure. The two radio relics have unusually flat integrated spectral indices of -0.49 +/- 0.18 and -0.76 +/- 0.17, values that cannot be easily reconciled with the theory of standard diffusive shock acceleration of thermal particles at weak merger shocks. We present imaging results from XMM-Newton and Chandra observations of the cluster, aimed to detect and characterise density discontinuities in the ICM. As expected, we detect a density discontinuity near …
We present an analysis of the merging cluster MACS J1149.5+2223 using archival imaging from Subaru/Suprime-Cam and multi-object spectroscopy from Keck/DEIMOS and Gemini/GMOS. We employ two and three dimensional substructure tests and determine that MACS J1149.5+2223 is composed of two separate mergers between three subclusters occurring $\sim$1 Gyr apart. The primary merger gives rise to elongated X-ray morphology and a radio relic in the southeast. The brightest cluster galaxy is a member of the northern subcluster of the primary merger. This subcluster is very massive (16.7$^{+\text{1.25}}_{…
We report the discovery of twin radio relics in the outskirts of the low-mass merging galaxy cluster Abell 168 (redshift=0.045). One of the relics is elongated with a linear extent $\sim$ 800 kpc, a projected width of $\sim$ 80 kpc and is located $\sim$ 900 kpc toward the north of the cluster center, oriented roughly perpendicular to the major axis of the X-ray emission. The second relic is ring-shaped with a size $\sim$ 220 kpc and is located near the inner edge of the elongated relic at a distance of $\sim$ 600 kpc from the cluster center. These radio sources were imaged at 323 and 608 MHz w…
Galaxy clusters undergo mergers that can generate extended radio sources called radio relics. Radio relics are the consequence of merger-induced shocks that propagate in the intra cluster medium (ICM). In this paper we analyse the radio, optical and X-ray data from a candidate galaxy cluster that has been selected from the radio emission coming from a candidate radio relic detected in NRAO VLA Sky Survey (NVSS). Our aim is to clarify the nature of this source and prove that under certain conditions radio emission from radio relics can be used to trace relatively low-mass galaxy clusters. We ha…
Radio relics are patches of diffuse synchrotron radio emission that trace shock waves. Relics are thought to form when intra-cluster medium electrons are accelerated by cluster merger induced shock waves through the diffusive shock acceleration mechanism. In this paper, we present observations spanning 150 MHz to 30 GHz of the `Sausage' and `Toothbrush' relics from the Giant Metrewave and Westerbork telescopes, the Karl G. Jansky Very Large Array, the Effelsberg telescope, the Arcminute Microkelvin Imager and Combined Array for Research in Millimeter-wave Astronomy. We detect both relics at 30…
Radio relics are Mpc-sized synchrotron sources located in the peripheral regions of galaxy clusters. Models based on the diffuse shock acceleration (DSA) scenario have been widely accepted to explain the formation of radio relics. However, a critical challenge to these models is that most observed shocks seem too weak to generate detectable emission, unless fossil electrons, a population of mildly energetic electrons that have been accelerated previously, are included in the models. To address this issue, we present a new semi-analytical model to describe the formation and evolution of radio r…
Multi-Wavelength Signatures of a Giant Cometary Radio Halo in MACSJ0417-1154
National Centre for Radio Astrophysics, Tata Institute of Fundamental Research（塔塔基础研究所国家射电天体物理中心）；International Centre for Theoretical Sciences, Tata Institute of Fundamental Research（塔塔基础研究所国际理论科学中心）；Dipartimento di Fisica e Astronomia (DIFA), Università di Bologna（博洛尼亚大学物理与天文系）；Istituto Nazionale di Astrofisica – Istituto di Astrofisica Spaziale e Fisica Cosmica (IASF)（意大利国家天体物理研究所空间天体物理与宇宙物理学研究所）
We observed the cluster CIZA J2242.8+5301 with the Arcminute Microkelvin Imager at $16$ GHz and present the first high radio-frequency detection of diffuse, non-thermal cluster emission. This cluster hosts a variety of bright, extended, steep-spectrum synchrotron-emitting radio sources, associated with the intra-cluster medium, called radio relics. Most notably, the northern, Mpc-wide, narrow relic provides strong evidence for diffusive shock acceleration in clusters. We detect a puzzling, flat-spectrum, diffuse extension of the southern relic, which is not visible in the lower radio-frequency…
Superclusters are the largest objects in the Universe, and they provide a unique opportunity to study how galaxy clusters are born at the junction of the cosmic web as well as the distribution of magnetic fields and relativistic particles beyond cluster volume. The field of radio astronomy is going through an exciting and important era of the Square Kilometer Array (SKA). We now have the most sensitive functional radio telescopes, such as the MeerKAT, which offers high angular resolution and sensitivity towards diffuse and faint radio sources. To study the radio environments around supercluste…
Wiggling Through the ICM: Multi-Resolution Radio Imaging of a Tailed Radio Galaxy in MACS J1354.6+7715
Durham University（杜伦大学）；Indian Institute of Science Education and Research Mohali（印度科学教育研究所莫哈利分校）；Institute for Computational Cosmology, Department of Physics, Durham University（杜伦大学物理学院计算宇宙学研究所）；National Centre for Radio Astrophysics, TIFR（印度天文物理国家射电中心，塔塔基础研究院）；Centre for Space Research, North-West University（西北大学空间研究中心）
Cluster mergers leave distinct signatures in the ICM in the form of shocks and diffuse cluster radio sources that provide evidence for the acceleration of relativistic particles. However, the physics of particle acceleration in the ICM is still not fully understood. Here we present new 1-4 GHz Jansky Very Large Array (VLA) and archival Chandra observations of the HST Frontier Fields Cluster Abell 2744. In our new VLA images, we detect the previously known $\sim2.1$ Mpc radio halo and $\sim1.5$ Mpc radio relic. We carry out a radio spectral analysis from which we determine the relic's injection…
Detailed observations of star forming galaxies at high redshift are critical to understand the formation and evolution of the earliest galaxies. Gravitational lensing provides an important boost, allowing observations at physical scales unreachable in unlensed galaxies. We present three lensed galaxies from the RELICS survey at $z_{phot} = 6 - 10$, including the most highly magnified galaxy at $z_{phot} \sim 6$ (WHL0137-zD1, dubbed the Sunrise Arc), the brightest known lensed galaxy at $z_{phot} \sim 6$ (MACS0308-zD1), and the only spatially resolved galaxy currently known at $z_{phot} \sim 10…
Radio relics at the peripheries of galaxy clusters are tracers of the elusive cluster merger shocks. We report the discovery of a single radio relic in the galaxy cluster PLCK G200.9-28.2 ($z=0.22$, $M_{500} = 2.7\pm0.2 \times 10^{14} M_{\odot}$) using the Giant Metrewave Radio Telescope at 235 and 610 MHz and the Karl G. Jansky Very Large Array at 1500 MHz. The relic has a size of $\sim 1 \times 0.28$ Mpc, an arc-like morphology and is located at 0.9 Mpc from the X-ray brightness peak in the cluster. The integrated spectral index of the relic is $1.21\pm0.15$. The spectral index map between 2…
Diffuse radio emission in galaxy clusters is known to be related to cluster mass and cluster dynamical state. We collect the observed fluxes of radio halos, relics, and mini-halos for a sample of galaxy clusters from the literature, and calculate their radio powers. We then obtain the values of cluster mass or mass proxies from previous observations, and also obtain the various dynamical parameters of these galaxy clusters from optical and X-ray data. The radio powers of relics, halos, and mini-halos are correlated with the cluster masses or mass proxies, as found by previous authors, with the…
Observations of radio relics at very high frequency (>10 GHz) can help to understand how particles age and are (re-)accelerated in galaxy cluster outskirts and how magnetic fields are amplified in these environments. In this work, we present new single-dish 18.6 GHz Sardinia Radio Telescope and 14.25 GHz Effelsberg observations of the well known northern radio relic of CIZA J2242.8+5301. We detected the relic which shows a length of $\sim$1.8 Mpc and a flux density equal to $\rm S_{14.25\,GHz}=(9.5\pm3.9)\,mJy$ and $\rm S_{18.6\,GHz}=(7.67\pm0.90)\,mJy$ at 14.25 GHz and 18.6 GHz respectively. …
The remnant radio galaxies in galaxy clusters are important sources of seed relativistic electron population in the intra-cluster medium (ICM). Their occurrence and spectral properties are poorly studied. In this work we present a broadband study of the radio relic in the galaxy cluster Abell 4038 using the Upgraded Giant Metrewave Radio Telescope (uGMRT). We present the uGMRT images in the bands 300 - 500 MHz and 1050 - 1450 MHz having rms noise $70\,μ$Jy beam$^{-1}$ and $30\,μ$Jy beam$^{-1}$, respectively, that are the deepest images of this field so far. A spectral analysis of the relic ove…
We present a radio and X-ray analysis of the galaxy cluster SPT-CL J2032-5627. Investigation of public data from the Australian Square Kilometre Array Pathfinder (ASKAP) at 943 MHz shows two previously undetected radio relics at either side of the cluster. For both relic sources we utilise archival Australia Telescope Compact Array (ATCA) data at 5.5 GHz in conjunction with the new ASKAP data to determine that both have steep integrated radio spectra ($α_\mathrm{SE} = -1.52 \pm 0.10$ and $α_\mathrm{NW,full} = -1.18 \pm 0.10$ for the southeast and northwest relic sources, respectively). No shoc…
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）
Diffuse radio emission from galaxy clusters in the form of radio halos and relics are tracers of the shocks and turbulence in the intra-cluster medium. The imprints of the physical processes that govern their origin and evolution can be found in their radio morphologies and spectra. The role of mildly relativistic population of electrons may be crucial for the acceleration mechanisms to work efficiently. Low frequency observations with telescopes that allow imaging of extended sources over a broad range of low frequencies ($< 2$ GHz) offer the best tools to study these sources. I will review t…
Abell 3266 is a massive and complex merging galaxy cluster that exhibits significant substructure. We present new, highly sensitive radio continuum observations of Abell 3266 performed with the Australian Square Kilometre Array Pathfinder (0.8$-$1.1 GHz) and the Australia Telescope Compact Array (1.1$-$3.1 GHz). These deep observations provide new insights into recently-reported diffuse non-thermal phenomena associated with the intracluster medium, including a 'wrong-way' relic, a fossil plasma source, and an as-yet unclassified central diffuse ridge, which we reveal comprises the brightest pa…
Radio relics are diffuse radio sources observed in galaxy clusters, probably produced by shock acceleration during cluster-cluster mergers. Their large size, of the order of 1 Mpc, indicates that the emitting electrons need to be (re)accelerated locally. The usually invoked Diffusive Shock Acceleration models have been challenged by recent observations and theory. We report the discovery of complex radio emission in the Galaxy cluster PLCKG287.0 +32.9, which hosts two relics, a radio halo, and several radio filamentary emission. Optical observations suggest that the cluster is elongated, likel…
Despite progress in understanding radio relics, there are still open questions regarding the underlying particle acceleration mechanisms. In this paper we present deep 1--4 GHz VLA observations of CIZA\,J2242.8+5301 ($z=0.1921$), a double radio relic cluster characterized by small projection on the plane of the sky. Our VLA observations reveal, for the first time, the complex morphology of the diffuse sources and the filamentary structure of the northern relic. We discover new faint diffuse radio emission extending north of the main northern relic. Our Mach number estimates for the northern an…
Although a merging galaxy cluster is a useful laboratory to study many important astrophysical processes and fundamental physics, only limited interpretations are possible without careful analysis of the merger scenario. However, the study is demanding because a thorough comparison of multi-wavelength observations with detailed numerical simulations is required. In this paper, we present such a study for the off-axis binary merger A115. The system possesses a number of remarkable observational features, but no convincing merger scenario, explaining the shape and location of the radio relic in …
We aim to carry out a radio study of the SoUthern Cluster sCale Extended Source Survey (SUCCESS) sample consisting of twenty massive (M$_{500} > 5\times10^{14}$ M$_{\odot}$), nearby (redshift $<0.3$) and southern ($-50^{\circ} < δ< -30^\circ$) galaxy clusters detected by the Planck satellite and the South Pole Telescope. Here we report targeted GMRT observations (325/610 MHz) for a sub-sample of nine clusters. We also use the first data release of MeerKAT Galaxy Cluster Legacy Survey (1283 MHz) for five of these nine clusters. The properties of the mini-halo in RXC J0528.9-3927, a candidate mi…
We have studied radio haloes and relics in nine merging galaxy clusters using the Murchison Widefield Array (MWA). The images used for this study were obtained from the GaLactic and Extragalactic All-sky MWA (GLEAM) Survey which was carried out at 5 frequencies, viz. 88, 118, 154, 188 and 215 MHz. We detect diffuse radio emission in 8 of these clusters. We have estimated the spectra of haloes and relics in these clusters over the frequency range 80-1400 MHz; the first such attempt to estimate their spectra at low frequencies. The spectra follow a power law with a mean value of $α= -1.13\pm0.21…
We present the discovery of a single radio relic located at the edge of the galaxy cluster A2384, using the MeerKAT radio telescope. A2384 is a nearby ($z$ = 0.092), low mass, complex bimodal, merging galaxy cluster that displays a dense X-ray filament ($\sim$ 700 kpc in length) between A2384(N) (Northern cluster) and A2384(S) (Southern cluster). The origin of the radio relic is puzzling. By using the MeerKAT observation of A2384, we estimate that the physical size of the radio relic is 824 $\times$ 264 kpc$^{2}$ and that it is a steep spectrum source. The radio power of the relic is $P_{1.4\m…
The galaxy cluster Abell 2256 hosts one of the most intriguing examples in the class of radio relics. It has been found that this radio relic has a rather flat integrated spectrum at low frequencies that would imply an injection spectral index for the electrons that is inconsistent with the flattest allowed by the test particle diffusive shock acceleration (DSA). We performed new high-frequency observations at 2273, 2640, and 4850 MHz. Combining these new observations with images available in the literature, we constrain the radio integrated spectrum of the radio relic in Abell 2256 over the w…
We observed three radio relics in galaxy clusters and one radio relic candidate at 4.85 and 8.35 GHz in total emission and linearly polarized emission with the Effelsberg 100-m telescope and one radio relic candidate in X-rays with the Chandra telescope. The radio spectra of the integrated emission below 8.35 GHz can be well fitted by single power laws for all four relics. The flat spectra (spectral indices of 0.9 and 1.0) for the "Sausage" relic in cluster CIZA J2242+53 and the "Toothbrush" relic in cluster 1RXS 06+42 indicate that models describing the origin of relics have to include effect…
CIZA J2242.8+5301 is a post-core passage, binary merging cluster that hosts a large, thin, arc-like radio relic, nicknamed the `Sausage', tracing a relatively strong shock front. We perform spatially-resolved spectral fitting to the available radio data for this radio relic, using a variety of spectral ageing models, with the aim of finding a consistent set of parameters for the shock and radio plasma. We determine an injection index of $0.77^{+0.03}_{-0.02}$ for the relic plasma, significantly steeper than was found before. Standard particle acceleration at the shock front implies a Mach numb…
The results of long XMM-Newton X-ray observations of the NW radio relic of Abell 3667 are presented. A shock is detected at the sharp outer edge of the radio relic, both in the X-ray surface brightness and the temperature profiles. The Mach number is M = 2.54^+0.80_-0.43. The temperature jump at the shock is larger than expected from the density jump, which may indicate that a dynamically important magnetic field aligned primarily parallel to the shock front is present. The gas temperature rises gradually over several arc minutes within the shock region. This could indicate that the shock ener…
In this second paper of the Hawaii SCUBA-2 Lensing Cluster Survey series, we cross-match SCUBA-2 maps with 3 and 6 GHz images from the Janksy-VLA Frontier Fields Legacy Survey for three cluster fields, MACS J0416.1--2403, MACS J0717.5+3745, and MACS J1149.5+2223. Within the HST coverage, 14 out of 44 850 $μ$m sources have 3 GHz counterparts, five of which are also detected at 6 GHz. The 850 $μ$m flux densities of these detected sources span from 0.7 to 4.4 mJy after correcting for lensing amplification. The median redshift of the sample is $z = 1.28^{+0.07}_{-0.09}$, much lower than the typica…
