We study the dynamical status of the poor, low X-ray luminous galaxy clusters Abell 610, Abell 725, and Abell 796 (at z=0.1, 0.09, and 0.16, respectively), containing diffuse radio sources (relic, relic, and possible halo, respectively). Our analysis is based on new spectroscopic data obtained at the William Herschel Telescope for 158 galaxies, new photometry obtained at the Isaac Newton Telescope with the addition of data recovered from the Data Release 5 of the Sloan Digital Sky Survey. We use statistical tools to select 57, 36, and 26 cluster members and to analyze the kinematics of cluster galaxies, as well as to study the 2D cluster structure. The low values we compute for the global line-of-sight velocity dispersion of galaxies (420-700 km/s) confirm that these clusters are low-mass clusters. Abell 610 shows a lot of evidence of substructure. It seems to be formed by two structures separated by about 700 km/s in the cluster rest-frame, having comparable velocity dispersion (about 200 km/s) and likely causing a velocity gradient. The analysis of the 2D galaxy distribution shows a bimodal distribution in the core elongated in the SE-NW direction. Abell 725 and Abell 796, which are less sampled, show marginal evidence of substructure in the velocity space. They are elongated in the 2D galaxy distribution. For both Abell 610 and Abell 725 we shortly discuss the possible connection with the hosted diffuse radio relic. Our results show that relic radio sources are likely connected with merger events,but are not limited to massive clusters. About the possible halo source in Abell 796, there is some evidence of a merger event in this non-massive cluster, but a pointed radio observation is necessary to confirm this halo.
We present deep VLA observations of the galaxy clusters Abell 2256 and Abell 754, both of which appear to be in the violent stage of major cluster merger events. The complex nature of Abell 2256 is revealed through radio images which, in addition to the head-tail galaxies, show two extended, irregular, and sharp-edged regions of diffuse radio emission at the cluster periphery (so called radio relics), and a large-scale diffuse radio halo located in the central regions of the cluster. Polarimetry of the A2256 cluster relics reveals large-scale ordered magnetic fields which appear to trace the b…
We report extensive VLA and ATCA observations of the two diffuse radio sources in the cluster of galaxies Abell 548b, which confirm their classification as relics. The two relics (named A and B) show similar flux density, extent, shape, polarization and spectral index and are located at projected distances of about 430 and 500 kpc from the cluster center, on the same side of the cluster's X-ray peak. On the basis of spectral indices of discrete radio sources embedded within the diffuse features, we have attempted to distinguish emission peaks of the diffuse sources from unrelated sources. We h…
The Westerbork Northern Sky Survey (WENSS) and the NRAO/VLA Sky Survey (NVSS) were used to determine an upper limit to the diffuse radio flux from the nearby cluster Abell 2199. For the entire cluster, this limit is <3.25 Jy at 327 MHz from WENSS; for the inner 15' radius, the limit is <168 mJy at 1.4 GHz. These limits are used to constrain the cluster magnetic field by requiring that the radio flux be consistent with the hard X-ray (HXR) flux observed by BeppoSAX, assuming that the observed HXR excess is due to inverse Compton (IC) scattering of cosmic microwave background photons by relativi…
We have searched for diffuse intracluster light in the galaxy cluster Abell 2667 (z=0.233) from HST images in three filters. We have applied to these images an iterative multi-scale wavelet analysis and reconstruction technique, which allows to subtract stars and galaxies from the original images. We detect a zone of diffuse emission south west of the cluster center (DS1), and a second faint object (ComDif), within DS1. Another diffuse source (DS2) may be detected, at lower confidence level, north east of the center. These sources of diffuse light contribute to 10-15% of the total visible ligh…
Using drift scan data, a new approach to determining surface brightness profiles, and techniques for detecting low surface brightness signals, we fit the light profile of the brightest cluster galaxy (BCG) in the rich cluster Abell 1651 out to 670 h^{-1} kpc. This radius is a significant fraction of the virial radius of the cluster (2 h^{-1} Mpc; Girardi et al. 1998), indicating that the sizes of the BCG and the cluster are comparable. We find that the profile is consistent with a de Vaucouleurs profile over the radial range probed. We also find that the integrated light profile of the BCG in …
We report the first detection of an inverse Compton X-ray emission, spatially correlated with a very steep spectrum radio source (VSSRS), 0038-096, without any detected optical counterpart, in cluster Abell 85. The ROSAT PSPC data and its multiscale wavelet analysis reveal a large scale (linear diameter of the order of 500 h^{-1}_{50} kpc), diffuse X-ray component, in excess to the thermal bremsstrahlung, overlapping an equally large scale VSSRS. The primeval 3 K background photons, scattering off the relativistic electrons can produce the X-rays at the detected level. The inverse Compton flux…
We have examined the orientations of brightest cluster galaxies (BCGs) in poor MKW and AWM clusters and find that, like their counterparts in richer Abell clusters, poor cluster BCGs exhibit a strong propensity to be aligned with the principal axes of their host clusters as well as the surrounding distribution of nearby (< 20/h Mpc) Abell clusters. The processes responsible for dominant galaxy alignments are therefore independent of cluster richness. We argue that these alignments most likely arise from anisotropic infall of material into clusters along large-scale filaments.
From ROSAT data, the bright X-ray cluster Abell 85 was found to show a roughly symmetrical shape, on to which are superimposed several features, among which: (1) a blob or group of galaxies falling on to the main cluster, with the gas in the impact region probably hotter and the galaxies in that zone showing enhanced star formation; (2) a filament, either diffuse or made of small groups of galaxies, extending at least 4 Mpc from the cluster (Durret et al. 1998). Preliminary results obtained from XMM-Newton and Chandra observations of Abell 85 and its filament will be presented.
We present deep VLA observations of the merging galaxy cluster Abell 2256. This cluster is known to possess diffuse steep spectrum radio relic emission in the peripheral regions. Our new observations provide the first detailed image of the central diffuse radio halo emission in this cluster. The radio halo extends over more than 800 kpc in the cluster core, while the relic emission covers a region of ~1125 x 520 kpc. A spectral index map of the radio relic shows a spectral steepening from the northwest toward the southeast edge of the emission, with an average spectral index between 1369 MHz a…
We are undertaking a program to measure the characteristics of the intracluster light (total flux, profile, color, and substructure) in a sample of 10 galaxy clusters with a range of cluster mass, morphology, and redshift. We present here the methods and results for the first cluster in that sample, A3888. We have identified an intracluster light (ICL) component in A3888 in V and r that contains 13\pm5% of the total cluster light and extends to 700h_{70}^{-1}kpc (~0.3 r_{200}) from the center of the cluster. The ICL color in our smallest radial bin is V-r = 0.3 \pm 0.1, similar to the central …
We have undertaken a survey of H alpha emission in a substantially complete sample of CGCG galaxies of types Sa and later within 1.5 Abell radii of the centres of 8 low-redshift Abell clusters. Some 320 galaxies were surveyed, of which 116 were detected in emission (39% of spirals, 75% of peculiars). Detected emission was classified as `compact' or `diffuse'. From an analysis of the full survey sample, we reconfirm our previous identification of compact and diffuse emission with circumnuclear starburst and disk emission respectively. The circumnuclear emission is associated either with the pre…
We give an update of our ongoing survey for intracluster light (ICL), in a sample of distant Abell clusters. We find that the amount of intracluster starlight is comparable to that seen in nearby clusters, and that tidal debris appears to be common.
Clusters of galaxies may contain cluster-wide, centrally located, diffuse radio sources, called halos. They have been found to show morphologies similar to those of the X-ray emission. To quantify this qualitative statement we performed a point-to-point comparison of the radio and the X-ray emission for four clusters of galaxies containing radio halos: Coma, Abell 2255, Abell 2319, Abell 2744. Our study leads to a linear relation between the radio and the X-ray surface brightness in two clusters, namely Abell 2255 and Abell 2744. In Coma and A2319 the radio and the X-ray brightnesses seem to b…
We present VLA data at 330 MHz and 1.5 GHz of the radio emission observed in the cooling flow cluster A2626. By producing images at different resolutions we found that the radio source consists of different components: an unresolved core plus a jet-like feature, two elongated parallel features, and an extended diffuse emission (radio mini-halo). Low resolution images allow us to derive morphological and spectral information of the diffuse emission: the radio mini-halo is extended on a scale comparable to that of the cooling flow region and is characterized by amorphous morphology, lack of pola…
We have observed with XMM-Newton the extended 4 Mpc filament detected by the ROSAT PSPC in the neighbourhood of the cluster of galaxies Abell 85. We confirm that there is an extended feature, aligned at the same position angle as the major axis of the central cD, the bright cluster galaxies, and nearby groups and clusters. We find that the X-ray emission from the filament is best described by thermal emission with a temperature of about 2 keV, which is significantly lower than the ambient cluster medium, but is significantly higher than anticipated for a gas in a weakly bound extended filament…
We report a new analysis of diffuse EUV emission in clusters of galaxies. We find the cluster emission is strongly influenced by the variation of the telescope sensitivity over the field of view and upon the details of the subtraction of the EUV emission for the X-ray plasma. We investigate these effects on Abell 1795, Abell 2199, and the Coma cluster. When we use the appropriate correction factors, we find there is no evidence for any excess EUV emission in Abell 1795 or Abell 2199, However, we do find extended EUV emission in the Coma cluster and in the Virgo cluster using our new analysis p…
Using X-ray temperature and surface brightness profiles of the hot intracluster medium derived from ASCA and ROSAT observations we place constraints on the dark matter and baryon fraction distributions in the poor clusters Abell 1060 and AWM 7. Although their total mass distributions are similar, AWM 7 has twice the baryon fraction of Abell 1060 in the best-fit models. The functional form of the dark matter distribution is ill-determined, however mass models where the baryon fractions in Abell 1060 and AWM 7 significantly overlap are excluded. Such variations in baryon fraction are not predict…
As part of a continuing study of the effect of cluster environment on the star formation properties of galaxies, we have undertaken an H-alpha objective prism survey of the nearby cluster, Abell 1060. We detect 33 galaxies in emission, 24 of which are cluster members. We present new radial velocity measurements and H-alpha+[NII] equivalent widths and fluxes for a number of these galaxies. We distinguish between galaxies with diffuse and compact emission, the latter having been associated in previous work with a disturbed morphology of the galaxy and most likely resulting from tidally-induced s…
We study the distribution of X-ray selected clusters of galaxies with respect to superclusters determined by Abell clusters of galaxies and show that the distribution of X-ray clusters follows the supercluster-void network determined by Abell clusters. We find that in this network X-ray clusters are more strongly clustered than other clusters. Poor, non-Abell X-ray clusters follow the supercluster-void network as well: these clusters are embedded in superclusters determined by rich clusters and populate filaments between them. We present a new catalog of superclusters of Abell clusters out to …
A pilot study with the powerful new backend of the Westerbork Synthesis Radio Telescope (WSRT) of two galaxy clusters at z=0.2 has revealed neutral hydrogen emission from 42 galaxies. The WSRT probes a total combined volume of 3.4x10^4 Mpc^3 at resolutions of 54x86 kpc^2 and 19.7 km/s, surveying both clusters and the large scale structure in which they are embedded. In Abell 963, a dynamically relaxed, lensing Butcher-Oemler cluster with a high blue fraction, most of the gas-rich galaxies are located between 1 and 3 Mpc in projection, northeast from the cluster core. Their velocities are sligh…
We present WFPC2 images of the core of the cooling flow cD galaxy in Abell 1795. An irregular, asymmetric dust lane extends 7 \h75 kpc in projection to the north-northwest. The dust shares the morphology observed in the H$α$ and excess UV emission. We see both diffuse and knotty blue emission around the dust lane, especially at the ends. The dust and emission features lie on the edge of the radio lobes, suggesting star formation induced by the radio source or the deflection of the radio jets off of pre-existing dust and gas. We measure an apparent R$_V$ significantly less than 3.1, implying th…
New radio data is presented for the rich cluster Abell 2163. The cluster radio emission is characterized by the presence of a radio halo, which is one of the most powerful and extended halos known so far. In the NE peripheral cluster region, we also detect diffuse elongated emission, which we classify as a cluster relic. The cluster A2163 is very hot and luminous in X-ray. Its central region is probably in a highly non relaxed state, suggesting that this cluster is likely to be a recent merger. The existence of a radio halo in this cluster confirms that halos are associated with hot massive cl…
A pilot study with the powerful new backend of the Westerbork Synthesis Radio Telescope (WSRT) of two galaxy clusters at z=0.2 has revealed neutral hydrogen emission from 39 galaxies. The volume probed for each cluster is 1.7x10^4 Mpc^3, with spatial and velocity resolutions of 54x86 kpc^2 and 19.7 km/s, covering both clusters and the large scale structure in which they are embedded. The spatial distribution of the HI detected galaxies is very different for the two clusters. In Abell 963, most of the gas-rich galaxies are located to the northeast, at 1-3 Mpc from the cluster center in projecti…
The structure of the universe is believed to have formed by clustering hierarchically from small to large scales. Much of this evolution occurs very slowly but at a few special times more, rapid, violent activity may occur as major subunits collide at high velocities. The Abell 2125 complex (z=0.247) appears to be undergoing such an event as shown by modeling of the optical velocity field and by the detection with the VLA of an unusually large number of associated radio active galaxies. We present an 80 ksec Chandra imaging of Abell 2125, together with extensive complementary multi-wavelength …
New radio and X-ray data are reported for the rich cluster Abell 2255. The cluster radio emission is characterized by the presence of a diffuse halo source, located at the cluster center, and a more peripheral ridge of radio emission which could be a relic. In addition, 6 tailed radio sources and a small double are found to be associated with cluster galaxies. At X-ray wavelengths, the cluster shows elongated emission in the center, indicating an ongoing cluster merger, with the axis in the east-west to southeast-northwest direction. The overall cluster temperature is found from the ROSAT obse…
`Wakes' of X-ray emission have now been detected trailing behind a few (at least seven) elliptical galaxies in clusters. To quantify how widespread this phenomenon is, and what its nature might be, we have obtained a deep (70 ksec) X-ray image of the poor cluster Abell 160 using the ROSAT HRI. Combining the X-ray data with optical positions of confirmed cluster members, and applying a statistic designed to search for wake-like excesses, we confirm that this phenomenon is observed in galaxies in this cluster. The probability that the detections arise from chance is less than 0.0038. Further, th…
We present the current status of radio observations of several clusters of galaxies done with the 100-m telescope Effelsberg. The purpose of this still ongoing project is to obtain new sensitive single-dish measurements of large extended diffuse radio sources in these clusters. The use of a single-dish is required to recover all the flux. In this paper we present the current maps of the clusters Coma, Abell 2256 and Abell 2163.
We present a study of the spectral, polarimetric, morphological and environmental properties of the diffuse radio source 0809+39 using observations taken with the Westerbork Synthesis Radio Telescope, the Very Large Array, and archival optical and X-ray data. The source has two distinct diffuse, steep-spectrum components, one in the north that is highly polarized, and a linear southern component undetected in polarization. We discuss several plausible origins for each component, and conclude that the northern bright polarized component is most likely a radio relic associated with a poor z$\sim…
We present a long BeppoSAX observation of Abell 754 that reports a nonthermal excess with respect to the thermal emission at energies greater than ~45 keV. A VLA radio observation at 1.4 GHz definitely confirms the existence of diffuse radio emission in the central region of the cluster, previously suggested by images at 74 and 330 MHz (Kassim et al 2001), and reports additional features. Besides, our observation determines a steeper radio halo spectrum in the 330-1400 MHz frequency range with respect to the spectrum detected at lower frequencies, indicating the presence of a spectral cutoff. …
The connection of cluster mergers with the presence of extended, diffuse radio sources in galaxy clusters is still debated. An interesting case is the rich, merging cluster Abell 520, containing a radio halo. A recent gravitational analysis has shown in this cluster the presence of a massive dark core suggested to be a possible problem for the current cold dark matter paradigm. We aim to obtain new insights into the internal dynamics of Abell 520 analyzing velocities and positions of member galaxies. Our analysis is based on redshift data for 293 galaxies in the cluster field obtained combinin…
We present 83 new galaxy radial velocities in the field of 18 APM clusters with redshifts between 0.06 and 0.13. The clusters have Abell identifications and the galaxies were selected within 0.75 h$^{-1}$Mpc in projection from their centers. We derive new cluster velocity dispersions for 13 clusters using our data and published radial velocities. We analyze correlations between cluster velocity dispersions and cluster richness counts as defined in Abell and APM catalogs. The correlations show a statistically significant trend although with a large scatter suggesting that richness is a poor est…
We present 74 MHz and 330 MHz VLA observations of Abell 754. Diffuse, halo-like emission is detected from the center of the cluster at both frequencies. At 330 MHz the resolution of 90'' distinguishes this extended emission from previously known point sources. In addition to the halo and at a much lower level, outlying steep-spectrum emission regions straddle the cluster center and are seen only at 74 MHz. The location, morphology and spectrum of this emission are all highly suggestive of at least one, and possibly two cluster radio relics. Easily obtained higher resolution, higher sensitivity…
This series of papers explores the evolution of late-type galaxies in the rich cluster Abell 85. Here, we revisit the complex dynamical state of A 85 by using independent methods. We analyze the redshift distribution towards the cluster out to 40,000 km/s, and determine the mean redshifts of the background clusters A 87 and A 89. We then search for substructures in A 85 by considering the 2-D galaxy distribution for its members and by applying the kinematical 3-D Delta-test to both projected positions and radial velocities. This clearly reveals several substructures that we describe. We also a…
In this paper we report on the analysis of a deep ROSAT HRI image of the moderately-rich cluster, Abell 2634, by which we have been able to detect the X-ray emission from the galaxies in the cluster. The ICM of Abell 2634 is an order of magnitude denser than that of the Virgo cluster, and so this analysis allows us to explore the X-ray properties of individual galaxies in the richest environment yet explored. By stacking the X-ray images of the galaxies together, we have shown that their emission appears to be marginally resolved by the HRI. This extent is smaller than for galaxies in poorer e…
We report the serendipitous discovery of a large HI cloud with an associated HI mass of $6(\pm1.5)\times 10^9 h^{-2}$ M$_\odot$ and a heliocentric velocity 8800 \kms, located near the periphery of the cluster of galaxies Abell 2634. Its velocity field appears to be very quiescent, as no gradients in the peak velocity are seen over its extent of 143$ h^{-1}$ by 103$ h^{-1}$ kpc. The distribution of gas is poorly resolved spatially, and it is thus difficult at this time to ascertain the nature of the cloud. At least two relatively small, actively star--forming galaxies appear to be embedded in t…
We report optical spectroscopic observations of RX J0018.8+1602, a ROSAT X-ray source proposed to be an intermediate redshift cluster of galaxies. Our observations confirm the identification of RX J0018.8+1602 and provide measurements of its mean radial velocity (z=0.5406 +/- 0.0006) and velocity dispersion (sigma_p = 200 [+110, -80] km/s). This is the second poor cluster that has been found to be a companion to CL 0016+16 (z=0.5455), the other one being RX J0018.3+1618 (z=0.5506). The 0.2-2 keV band source-frame X-ray luminosity summed over both companion clusters is 5E44 ergs/s, which is a s…
We present an 82 ksec Chandra ACIS-I observation of a large-scale hierarchical complex, which consists of various clusters/groups of galaxies and low-surface brightness X-ray emission at z = 0.247. This high-resolution {\sl Chandra} observation allows us for the first time to separate unambiguously the X-ray contributions from discrete sources and large-scale diffuse hot gas. We detect 99 X-ray sources in a $17^\prime \times 17^\prime$ field. Ten of these sources are identified as members of the complex and are mostly radio-bright. Whereas unresolved X-ray sources tend to be associated with ga…
We have detected an X-ray absorption feature against the core of the galaxy cluster Abell 2029 (z=0.0767) which we identify with the foreground galaxy UZC J151054.6+054313 (z=0.0221). Optical observations (B, V, R, and I) indicate that it is an Scd galaxy seen nearly edge-on at an inclination of 87 \pm 3 degrees. HI observations give a rotation velocity of 108 kms and an atomic hydrogen mass of M_{HI} = 3.1 X 10^9 d_{90}^2 \msun, where d_{90} is the distance to the galaxy in units of 90 Mpc. X-ray spectral fits to the Chandra absorption feature yield a hydrogen column density of (2.0 \pm 0.4) …
We present the composite luminosity function (hereafter LF) of galaxies for 81 Abell clusters studied in our survey of the Northern Hemisphere, using DPOSS data processed by the CRoNaRio collaboration. The derived LF is very accurate due to the use of homogeneous data both for the clusters and the control fields and to the local estimate of the background, which takes into account the presence of large-scale structures and of foreground clusters and groups. The global composite LF is quite flat down to $M^*+5$ has a slope $α\sim-1.0\pm0.2$ with minor variations from blue to red filters, and $M…
Abell 2256 is a nearby (z~0.06), rich cluster of galaxies with fascinating observed properties across a range of wavelengths. Long believed to represent a cluster merger, recent X-ray and optical results have suggested that in addition to the primary cluster and subcluster there is evidence for a third, poorer system. We present wide-field, high sensitivity 1.4 GHz VLA radio observations of Abell 2256 in conjunction with optical imaging and additional spectroscopy. Over 40 cluster radio galaxies are identified, with optical spectroscopy indicating the emission source (star formation or AGN) fo…
We have discovered new diffuse radio sources likely associated with groups of galaxies at low redshift (0.01-0.04) and without apparent AGN by using the WENSS and WISH catalogs to perform an unbiased survey. These sources resemble the radio halos, mini-halos, and 'relics' of rich clusters, which are thought to be powered by shocks and turbulence from infall into their deep potential wells. Our detection of similar sources within the shallow potential wells of groups of galaxies challenges this model. Their radio luminosities are approximately two orders of magnitude higher than expected from t…
We present the composite luminosity function (hereafter LF) of galaxies for 80 Abell clusters studied in our survey of the Northern Hemisphere, using DPOSS data in the framework of the CRoNaRio collaboration. Our determination of the LF has been computed with very high accuracy thanks to the use of homogeneous data both for the clusters and the control fields and to a local estimate of the background, which takes into account the presence of large-scale structures and of foreground clusters and groups. The global composite LF is quite flat down to M^+5 and it has a slope alpha=-1.0 +/- 0.2 wit…
We report the detection by Chandra of SMM J02399-0134 and SMM J02399-0136, two distant (z=1.06 and z=2.81, respectively) submillimeter sources gravitationally magnified by the galaxy cluster Abell 370. These are high-significance (> 7-sigma) X-ray detections of the high-redshift submillimeter source population. The X-ray positions are coincident with the optical positions to within one arcsecond. The X-ray spectra, while of low signal-to-noise ratio, are quite hard. Absorbed power law models with fixed photon indices of $Γ=2.0$ imply local absorbing columns $>2 \times 10^{23}$ cm$^{-2}$ and un…
Large-scale fluctuations of the X-ray background are investigated using the ROSAT All-Sky Survey. The autocorrelation function of the extragalactic background at 1 keV is determined at separations 0.1 - 40 deg. We detect a significant signal for separations < 6 deg, which is larger than previous upper limits. We analyse the cross-correlation between the angular positions of Abell clusters of galaxies and the intensity of the X-ray background. The cross-correlation extends to several degrees for clusters of distance class .leq. 4. We conclude that Abell clusters are associated with extended, lo…
We present the results of a search for Extreme Ultraviolet emission in A4059, a cluster with an X-ray emitting cluster gas. Our analysis of Extreme Ultraviolet Explorer (EUVE) Deep Survey observations of this cluster shows that it is associated with diffuse EUV emission. Outside the central 2 arcmin radius the entire EUV emission detected is explained by the low energy tail of the X-ray emitting gas. Within the central 2 arcmin region of the cluster we find a deficit of EUV emission compared to that expected from the X-ray gas. This flux deficit is discussed in the context of the cluster's coo…
We studied the temperature and abundance distributions of intra-cluster medium (ICM) in the Abell 262 cluster of galaxies observed with Suzaku. Abell 262 is a bright, nearby poor cluster with ICM temperature of ~2 keV, thus providing useful information about the connection of ICM properties between groups and clusters of galaxies. The observed spectrum of the central region was well-represented by two temperature models, and the spectra for the outer regions were described by single temperature model. With the XIS instrument, we directly measured not only Si, S, and Fe lines but also O and Mg …
Clusters of galaxies are among the best candidates for particle acceleration sources in the universe, a signature of which is non-thermal hard X-ray emission from the accelerated relativistic particles. We present early results on Suzaku observations of non-thermal emission from Abell 3376, which is a nearby on-going merger cluster. Suzaku observed the cluster twice, focusing on the cluster center containing the diffuse radio emission to the east, and cluster peripheral region to the west. For both observations, we detect no excess hard X-ray emission above the thermal cluster emission. An upp…
We present the analysis of pointed ROSAT PSPC observations of five of the most luminous, intermediate redshift ($0.1 < z < 0.15$) clusters of galaxies detected in the ROSAT All-Sky Survey. The PSPC data are combined with optical CCD images and spectra to examine the relationship between clusters and their central cluster galaxies (CCGs). Abell 1068, Abell 1361 and Abell 1664 contain three of the most optically line-luminous CCGs known. The PSPC X-ray data show that these galaxies lie at the centres of massive (200 -- 400 solar masses per year) cooling flows. The alignment between CCGs and thei…
The theory predicts that the effect of gravitational lensing by the matter associated with clusters of galaxies can magnify background sources, leading to an enhancement of source number density around foreground clusters of galaxies. We conduct a search for the associations of distant radio-bright quasars with Abell clusters using the 1-Jy and 2-Jy all-sky catalogs. Statistics turns to be very poor on the basis of the 1-Jy sample, which shows no correlations between the distant radio quasars with the foreground Abell clusters above $1σ$ level. However, an apparent association ($>1σ$) of the 2…
We present the nonuniform distribution of temperature and abundance in the angular extent of 10'(1.4 Mpc) in A1650 observed by XMM-Newton. Spectral analysis was carried out in 19 systematically-subdivided regions, and in 15 specified regions referred to the hardness ratio (HR) map. The value of HR, defined as the ratio of counts in the 1.6-10 keV band to those in the 0.8-1.6 keV, is an indicator to investigate the spatial variation of spectral features. The temperature and abundance were obtained to be 4-6 keV and 0.2-0.5 solar value with average values of 5.62+0.05-0.07 keV and 0.36+0.02-0.01…
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_{50}^{-1} 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 ra…
We have analyzed the Chandra, BeppoSax, and ROSAT observations of Abell 754 and report evidence of a soft, diffuse X-ray component. The emission is peaked in the cluster center and is detected out to 8' from the X-ray center. Fitting a thermal model to the combined BeppoSax and PSPC spectra show excess emission below 1 keV in the PSPC and above 100 keV in the BeppoSax PDS. The source 26W20 is in the field of view of the PDS. The addition of a powerlaw with the spectral parameters measured by Silverman et al. (1998) for 26W20 successfully models the hard component in the PDS. The remaining exce…
In this letter we present calibrated mass and light profiles of the rich cluster of galaxies Abell 1689 out to 1 $h^{-1}$ Mpc from the center. The high surface density of faint blue galaxies at high redshift, selected by their low surface brightness, are unique tools for mapping the projected mass distribution of foreground mass concentrations. The systematic gravitational lens distortions of $10^4$ of these background galaxies in 15\arcmin\ fields reveal detailed mass profiles for intervening clusters of galaxies, and are a direct measure of the growth of mass inhomogeneity. The mass is measu…
We use radio, near-IR, optical, and X-ray observations to examine dynamic processes in the central region of Abell 2125. In addition to the central triple, including members of both major dynamical subsystems identified from a redshift survey, this region features a galaxy showing strong evidence for ongoing gas stripping during a high-velocity passage through the gas in the cluster core. The disk galaxy C153 exhibits a plume stretching toward the cluster center seen in soft X-rays by Chandra, parts of which are also seen in [O II] emission and near-UV continuum light. HST imaging shows a dist…
We present the analysis of a Chandra observation of the galaxy cluster Abell 133, which has a cooling flow core, a central radio source, and a diffuse, filamentary radio source which has been classified as a radio relic. The X-ray image shows that the core has a complex structure. The most prominent feature is a "tongue" of emission which extends from the central cD galaxy to the northwest and partly overlaps the radio relic. One possibility is that this tongue is produced by Kelvin-Helmholtz (KH) instabilities through the interaction between the cold gas around the cD galaxy and hot intraclus…
We conduct an intensive study of the rich, X-ray luminous, and hot galaxy cluster Abell 697 (at z=0.282), likely containing a diffuse radio emission, to determine its dynamical status. Our analysis is based on new spectroscopic data obtained at the TNG telescope for 93 galaxies and on new photometric data obtained at the INT telescope. We combine galaxy velocity and position information to select 68 cluster members, determine global dynamical properties, and detect possible substructures. The investigation of the dynamical status is also performed by using X-ray data stored in the Chandra arch…
