Radio observations of the merging galaxy cluster system Abell 3391-Abell 3395 (original) (raw)
Related papers
A merger mystery: no extended radio emission in the merging cluster Abell 2146
Monthly Notices of the Royal Astronomical Society: Letters, 2011
We present a new 400 ks Chandra X-ray observation and a GMRT radio observation at 325 MHz of the merging galaxy cluster Abell 2146. The Chandra observation reveals detailed structure associated with the major merger event including the Mach M = 2.1 ± 0.2 bow shock located ahead of the dense subcluster core and the first known example of an upstream shock (M = 1.6 ± 0.1). Surprisingly, the deep GMRT observation at 325 MHz does not detect any extended radio emission associated with either shock front. All other merging galaxy clusters with X-ray detected shock fronts, including the Bullet cluster, Abell 520, Abell 754 and Abell 2744, and clusters with candidate shock fronts have detected radio relics or radio halo edges coincident with the shocks. We consider several possible factors which could affect the formation of radio relics, including the shock strength and the presence of a pre-existing electron population, but do not find a favourable explanation for this result. We calculate a 3σ upper limit of 13 mJy on extended radio emission, which is significantly below the radio power expected by the observed P radio − L X correlation for merging systems. The lack of an extended radio halo in Abell 2146 maybe due to the low cluster mass relative to the majority of merging galaxy clusters with detected radio halos.
Abell 1430: A merging cluster with exceptional diffuse radio emission
Astronomy & Astrophysics, 2021
Context. 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 close galaxy clusters. The mechanisms that may allow one to explain the high specific density of relativistic electrons, which are necessary to explain the radio luminosity of these bridge regions, have been poorly explored until now. Aims. When inspecting the first data release of the LOFAR Two-Metre Sky Survey (LoTSS), we discovered diffuse radio emission in the galaxy cluster Abell 1430. Here, we aim to determine the dynamical state of the cluster and characterise the diffuse radio emission. Methods. We analysed the LoTSS data in detail and complemented them with recent Karl G. Jansky Very Large Array observat...
Interactions of radio galaxies and the intracluster medium in Abell 160 and Abell 2462
Monthly Notices of The Royal Astronomical Society, 2005
We present Chandra and Very Large Array observations of two galaxy clusters, Abell 160 and Abell 2462, whose brightest cluster galaxies (BCGs) host wide angle tailed radio galaxies (WATs). We search for evidence of interactions between the radio emission and the hot, X-ray emitting gas, and we test various jet termination models. We find that both clusters have cool BCGs at the cluster centre, and that the scale of these cores (~30-40 kpc for both sources) is of approximately the same scale as the length of the radio jets. For both sources, the jet flaring point is coincident with a steepening in the host cluster's temperature gradient, and similar results are found for 3C 465 and Hydra A. However, none of the published models of WAT formation offers a satisfactory explanation as to why this may be the case. Therefore, it is unclear what causes the sudden transition between the jet and the plume. Without accurate modelling, we cannot ascertain whether the steepening of the temperature gradient is the main cause of the transition, or merely a tracer of an underlying process.
The Cluster Dynamics, X-Ray Emission, and Radio Galaxies in Abell 578 = Abell 1569
The Astronomical Journal, 1997
We present the results of our multiwavelength study of two nearby Abell clusters that contain extended tailed radio sources. From our analysis of archival PSPC X-ray data, VLA radio observations, and new velocity measurements, we find strong evidence that these clusters are not relaxed. Significant X-ray substructure is revealed by examining deviations from circular models of the overall X-ray surface brightness maps. We report 130 new redshifts from the fields of A578 and A1569 and find that 41 galaxies belong to A578 and 54 belong to A1569. Moreover, we detect the presence of substructure in the velocity and spatial distribution of galaxies. We identify two interacting subclusters in A578 and two gravitationally unbound subclusters in A1569. Furthermore, we find that the radio sources in A578 are at rest with respect to their subclusters and that the Wide-Angled Tailed (WAT) source in A1569 has a small peculiar motion with respect to its subcluster (220 km/s). The standard model of ram pressure induced jet curvature requires relative velocities of the radio sources with respect to the ICM of ∼ > 1000 km/s. Therefore, the apparent peculiar velocities of the radio galaxies can not explain the bending of the jets/tails for the Narrow-Angled Tailed (NAT) radio source in A578 and for the WAT in A1569. We suggest that a cluster-subcluster merger model provides a reasonable explanation for the X-ray and optical substructure detected in these systems.
New multi-wavelength (radio, optical & X-rays) observational evidences are presented which show that the nearby (z = 0.046), rich cluster of galaxies Abell 3376 is experiencing a major event of binary subcluster merger. The key evidence is the discovery of a pair of large, optically unidentified diffuse radio sources ('arcs'), symmetrically located about 2.6 h −1 50 Mpc apart at the opposite ends of the hot intra-cluster gas mapped by ROSAT in X-rays. It is argued that the gas-dynamical shock-waves, which occur naturally during cluster formation, are accelerating charged particles (cosmic rays) to relativistic energies, leading to synchrotron emission from the megaparsec scale radio arcs. If this is so, cluster Abell 3376 would also be a potential source capable of accelerating cosmic ray particles upto ultra-high energies (UHECR) of E max ∼ 10 18−19 eV. Thus this cluster is an excellent test-bed for understanding the physics of merger shocks and origin of enigmatic UHECR particles in structure formation process. Hence, Abell 3376 provides unique oppurtunities for further multi-wavelength observations with ground and space-borne observatories.
An elusive radio halo in the merging cluster Abell 781
Monthly Notices of The Royal Astronomical Society, 2011
Deep radio observations of the galaxy cluster Abell 781 have been carried out using the Giant Metrewave Radio Telescope at 325 MHz and have been compared to previous 610-MHz observations and to archival Very Large Array (VLA) 1.4-GHz data. The radio emission from the cluster is dominated by a diffuse source located at the outskirts of the X-ray emission, which we tentatively classify as a radio relic. We detected residual diffuse emission at the cluster centre at the level of S325 MHz˜ 15-20 mJy. Our analysis disagrees with Govoni et al., and on the basis of simple spectral considerations, we do not support their claim of a radio halo with the flux density of 20-30 mJy at 1.4 GHz. Abell 781, a massive and merging cluster, is an intriguing case. Assuming that the residual emission is indicative of the presence of a radio halo barely detectable at our sensitivity level, it could be a very steep spectrum source.
The Astronomical …, 2007
We present deep emission-line imaging taken with the new SOAR Optical Imaging Camera of the brightest cluster galaxy (BCG) in the nearby (z = 0.035) X-ray cluster of galaxies 2A0335+096. We also present our analysis of additional, multi-wavelength observations for the BCG, including long-slit optical spectroscopy, archival VLA radio data, Chandra X-ray imaging, and XMM UVimaging. Cluster 2A0335+096 is a bright, cool-core X-ray cluster, once known as a cooling flow. Within the highly disturbed core revealed by Chandra Xray observations, 2A0335+096 hosts a luminous and highly structured optical emission-line system, spanning the brightest cluster galaxy (BCG) and its companion. We confirm that the redshift of the companion is within 100 km s −1 of the BCG and has certainly interacted with the BCG, and is likely bound to it. The comparison of optical and radio images shows curved filaments in Hα emission surrounding the newly resolved radio source. The velocity structure of the emission-line bar between the BCG nucleus and the companion galaxy provides strong evidence for an interaction between the BCG and its northeast companion in the last ∼ 50 million years. The age of the radio source is similar to the interaction time, so this interaction may have provoked an episode of radio activity. We estimate a star formation rate of 7 M yr −1 from the Hα and archival UV arXiv:0705.1659v1 [astro-ph] 11 May 2007 -2data. This rate is similar to, but somewhat lower than, the revised X-ray cooling rate of 10 − 30 M yr −1 in the vicinity of the BCG, estimated from XMM spectra by . The Hα nebula is limited to a region of high X-ray surface brightness and cool X-ray temperatures. However, the detailed structures of Hα and X-ray gas differ. The peak of the X-ray surface brightness is not the peak of Hα emission, nor does it lie in the BCG. The estimated age of the radio lobes and their interaction with the optical emission-line gas, the estimated timescale for depletion and accumulation of cold gas, and the dynamical time in the system are all similar, suggesting a common trigger mechanism.
Radio emission at the centre of the galaxy cluster Abell 3560: evidence for core sloshing?
Astronomy & Astrophysics, 2013
Context. The present paper deals with the interplay between the radio emission associated with the dominant galaxy in clusters and the properties of the surrounding intracluster medium (ICM), studied on the basis of its X-ray emission. Aims. Previous radio observations of the galaxy cluster A 3560, located in the Shapley Concentration core, revealed the presence of complex radio emission associated with the brightest cluster member. To understand the origin of such radio emission we performed a detailed multiwavelength study, with high quality proprietary data in the radio and X-ray bands, and by means of optical data available in the literature. Methods. We observed the cluster with the Giant Metrewave Radio Telescope, the Very Large Array and the Australia Telescope Compact array at 240 and 610 MHz, 1.28, 1.4, 2.3, 4.8 and 8.4 GHz, and performed a detailed morphological and spectral study of the radio emission associated with the brightest cluster galaxy (BCG). Furthermore, we observed the cluster with the XM M -N ewton and Chandra observatories, to derive the properties of the intracluster gas. Finally, we made use of literature data to obtain the bidimensional distribution of the galaxies in the cluster. Results. The radio emission, associated with the north-eastern nucleus of the dumb-bell BCG, is the result of two components: an active radio galaxy, with jets and lobes, plus aged diffuse emission, which is not refurbished with new electrons at present. Our Chandra data show that the radio active nucleus of the BCG has extended X-ray emission, which we classify as a low-luminosity corona. A residual image of the XM M -N ewton brightness distribution shows the presence of a spiral-like feature, which we interpret as the signature of gas sloshing. The presence of a sub-group is clear in the surface brightness residual map, and it is supported also by the XM M -N ewton temperature analysis. The optical bidimensional analysis shows substructure in A 3560. A galaxy clump has been found at the location of the X-ray sub-group, and another group is present south of the cluster core, in the region where the spiral-like feature has been detected. The aged part of the radio emission closely follows the spiral pattern of the X-ray residual brightness distribution, while the two active radio lobes are bent in a completely different direction. We conclude that the complex radio emission associated with the cluster BCG is the result of a minor merger event in A 3560. The aged diffuse emission is strongly affected by the sloshing motion in the intracluster gas, and most likely bears information on the trajectory of the cluster BCG during the dynamical evolution of the cluster. On the other hand, the bent jets and lobes of the current radio AGN activity may reflect a complex gas velocity field in the innermost cluster regions and/or sloshing-induced oscillations in the motion of the cD galaxy.
Abell 3560, a galaxy cluster at the edge of a major merging event
Astronomy and Astrophysics, 2002
In this paper we study A3560, a rich cluster at the southern periphery of the A3558 complex, a chain of interacting clusters in the central part of the Shapley Concentration supercluster. From a ROSAT-PSPC map we find that the X-ray surface brightness distribution of A3560 is well described by two components, an elliptical King law and a more peaked and fainter structure, which has been modeled with a Gaussian. The main component, corresponding to the cluster, is elongated with the major axis pointing toward the A3558 complex. The second component, centered on the Dumb-bell galaxy which dominates the cluster, appears significantly offset (by ∼ 0.15 h −1 Mpc) from the cluster X-ray centroid. From a Beppo-SAX observation we derive the radial temperature profile, finding that the temperature is constant (at kT ∼ 3.7 keV) up to 8 arcmin, corresponding to 0.3 h −1 Mpc : for larger distances, the temperature significantly drops to kT ∼ 1.7 keV. We analyze also temperature maps, dividing the cluster into 4 sectors and deriving the temperature profiles in each sector: we find that the temperature drop is more sudden in the sectors which point towards the A3558 complex. From VLA radio data, at 20 and 6 cm, we find a peculiar bright extended radio source (J1332-3308), composed of a core (centered on the northern component of the Dumb-bell galaxy), two lobes, a "filament" and a diffuse component. The morphology of the source could be interpreted either by a strong interaction of the radio source with the intracluster medium or by the model of intermittency of the central engine.
arXiv: Astrophysics, 2002
New multi-wavelength (radio, optical & X-rays) observational evidencesare presented which show that the nearby (z = 0.046), rich cluster of galaxiesAbell 3376 is experiencing a major event of binary subcluster merger. Thekey evidence is the discovery of a pair of large, optically unidentified diffuseradio sources (‘arcs’), symmetrically located about 2.6h −150 Mpc apart at theopposite ends of the hot intra-cluster gas mapped by ROSAT in X-rays. Itis argued that the gas-dynamical shock-waves, which occur naturally duringcluster formation, are accelerating charged particles (cosmic rays) to relativis-tic energies, leading to synchrotron emission from the megaparsec scale radioarcs. If this is so, cluster Abell 3376 would also be a potential source capa-ble of accelerating cosmic ray particles upto ultra-high energies (UHECR) ofE max ∼ 10 18−19 eV. Thus this cluster is an excellent test-bed for understand-ing the physics of merger shocks and origin of enigmatic UHECR particlesin structur...