We present the final data from the spectroscopic survey of the ROSAT-ESO Flux-Limited X-ray (REFLEX) catalog of galaxy clusters. The REFLEX survey covers 4.24 steradians (34% of the entire sky) below a declination of 2.5 deg and at high Galactic latitude (|b| > 20 deg). The REFLEX catalog includes 447 entries with a median redshift of 0.08 and is better than 90% complete to a limiting flux fx = 3x10^{-12} erg s^{-1} cm^{-2} (0.1 to 2.4 keV), representing the largest statistically homogeneous sample of clusters drawn from the ROSAT All-Sky Survey (RASS) to date. Here we describe the details of the spectroscopic observations carried out at the ESO 1.5 m, 2.2 m, and 3.6 m telescopes, as well as the data reduction and redshift measurement techniques. The spectra typically cover the wavelength range 3600-7500 A at a FWHM resolution of ~14 A, and the measured redshifts have a total rms error of ~100 km s^{-1}. In total we present 1406 new galaxy redshifts in 192 clusters, most of which previously did not have any redshift measured. Finally, the luminosity/redshift distributions of the cluster sample and a comparison to the no-evolution expectations from the cluster X-ray luminosity function are presented.

ESO’s thermal infrared multi-mode instrument, had been decommissioned after Period 61, it got its very last chance on November 11th, 1998. The measurement was a special one, recording the lunar occultation of the well-known caryears ago, it turned out that measurements of lunar occultations may yield an angular resolution of about 30 milliseconds of arc (mas) at the wavelength of about 10 μm, similar to that expected for the VLTI. This would enable detailed studies of the distribution of circumstellar dust around evolved stars. Consequently, proposals were submitted which aimed at the derivation of the angular diameter of asymptotic-giant-branch (AGB) stars. Despite some difficulties that led to the loss of a few events, several light curves were acquired for infrared sources with 12 μm fluxes in the range of 5 . . . 50 Jy. Since the required time resolution is in the order of 20 . . . 40 ms, the measurements had to be performed in staring mode, i.e. without applying the chopping/nodding technique commonly used to eliminate the overwhelming thermal background. Furthermore, as a consequence of the limited number of frames, the predictions had to be accurate to within typically 15 . . . 20 seconds to catch the event, a condition that was not always met (primarily due to the positional errors for infrared sources, which went undetected in optical surveys). Moreover, the comparatively small FOV of TIMMI (18′′ × 18′′) in combination with the poor tracking of the telescope (close to the Moon or during daytime the auto-guider does not work!) always provided for sufficient challenges for the observing team. These measurements allowed the derivation of a few angular diameters and were crucial to assess the dependence of the attainable angular resolution on the signal-to-noise ratio. First results were presented at the ESO workshop Science

We present the final data from the spectroscopic survey of the ROSAT-ESO Flux-Limited X-ray (REFLEX) catalog of galaxy clusters. The REFLEX survey covers 4.24 steradians (34% of the entire sky) below a declination of 2.5 deg and at high Galactic latitude (|b| > 20 deg). The REFLEX catalog includes 447 entries with a median redshift of 0.08 and is better than 90% complete to a limiting flux fx = 3x10^{-12} erg s^{-1} cm^{-2} (0.1 to 2.4 keV), representing the largest statistically homogeneous sample of clusters drawn from the ROSAT All-Sky Survey (RASS) to date. Here we describe the details of the spectroscopic observations carried out at the ESO 1.5 m, 2.2 m, and 3.6 m telescopes, as well as the data reduction and redshift measurement techniques. The spectra typically cover the wavelength range 3600-7500 A at a FWHM resolution of ~14 A, and the measured redshifts have a total rms error of ~100 km s^{-1}. In total we present 1406 new galaxy redshifts in 192 clusters, most of which previously did not have any redshift measured. Finally, the luminosity/redshift distributions of the cluster sample and a comparison to the no-evolution expectations from the cluster X-ray luminosity function are presented.

We present X-ray and multi-frequency radio observations of the central radio sources in several X-ray cavity systems. We show that targeted radio observations are key to determining if the lobes are being actively fed by the central AGN. Low frequency observations provide a unique way to study both the lifecycle of the central radio source as well as its energy input into the ICM over several outburst episodes.

Aims. Using XMM Newton data, we investigate the nature of the X-ray emission in the radio relic 1253+275 in the Coma cluster. We determine the conditions of the cluster gas to check current models of relic formation, and we set constraints on the intracluster magnetic field. Methods. Both imaging and spectral analysis are performed, and the X-ray emission is compared with the radio emission. Results. We found that the emission is of thermal origin and is connected to the sub-group around NGC 4839. The best-fit gas temperature in the region of the relic and in its vicinity is in the range 2.8 - 4.0 keV, comparable to the temperature of the NGC 4839 sub-group. We do not detect any high temperature gas, resulting resulting from a possible shock in the region of the Coma relic. We therefore suggest that the main a source of energy for particles radiating in the radio relic is likely to be turbulence. From the X-ray data, we can also set a flux upper limit of 3.2 x 10(-13) erg cm(-2) s(-1), in the 0.3 - 10 keV energy range, to the non-thermal emission in the relic region. This leads to a magnetic field B > 1.05 mu G.

We present here a study of a sample of 14 nearby clusters of galaxies (0.06 < z < 0.1) observed with the ROSAT/PSPC. We convert the X-ray surface brightness profiles of the clusters into emission measure profiles scaled to the classical scaling relations based on the spherical collapse model. We sort the clusters into different temperature bins and stack the scaled emission measure (ScEM) profiles of clusters belonging to the same bin together. This method enhances the statistics of the profiles - especially in outer regions. The stacked profiles allow us to observe a signal out to radii r > r(200). Fitting beta-models to the overall ScEM profiles we find for the different sub-samples r(c) = 0.15 - 0.18r(200) and beta = 0.8, which is higher than the canonical value of beta = 2/3 often found. The beta-model is generally a better representation for hotter than for cooler clusters. We see indications for continuous steepening of the profiles with increasing radius: at radii r > 0.8r(200) the profiles are systematically below the beta-model curve with beta = 0.8.

A previous analysis of the Chandra X-ray image of the center of the cooling core cluster A2597 showed two "ghost holes'' in the X-ray emission to the west and northeast of the central radio galaxy PKS 2322 - 123. Previous radio observations did not detect any radio emission coming from the interior of the X- ray holes. We present new low-frequency radio observations of A2597. At 330 MHz, radio emission extends into the interior of the western ghost bubble, but not the northeast one. Our reanalysis of the archival Chandra data shows evidence for an X- ray tunnel ( elongated region of reduced X- ray emission) extending from near the center of the cD galaxy out to the west ghost bubble. We also detect a smaller X- ray hole to the northeast of the center of the cD and closer than the outer ghost bubbles. Radio observations at 1.3 GHz show extensions to the west along the X- ray tunnel toward the west ghost bubble, to the northeast into the new X- ray hole, and to the northwest. All of these structures are much larger than the two inner radio lobes seen previously at 8 GHz. The X- ray tunnel suggests that the west ghost bubble is part of a continuous flow of radio plasma out from the active galactic nucleus, rather than a detached buoyant old radio lobe, and thus it may be an intermediate case between an active radio galaxy and a buoyant lobe.

Clusters of galaxies contain a hot gas, which emits in X-rays. X-ray telescopes such as XMM-Newton allow to study this plasma to obtain information on physical quantities of these objects. We present here some results on the total mass density distribution of clusters obtained with XMM-Newton based on the hydrostatic approach. These results can be compared to models based on cold dark matter. Generally good agreement is found between observations and models. Furthermore we present a study on physical properties of a distant merging cluster of galaxies, which demonstrates the potential of XMM-Newton studies on this class of objects.

We present here a Study based on XMM-NEWTON data of RX J0256.5+0006, a medium distant (z=0.36) cluster of galaxies found in the Bright SHARC catalog. The X-ray emitting intracluster medium shows a bimodal structure: one main cluster component and a substructure in the west, which very likely falls onto the main cluster centre. The subcluster shows after Subtraction of the main cluster component a cometary shape pointing away from the main cluster centre, suggesting that ram pressure stripping is at work. Despite the indication of interaction between the two components we surprisingly do not find any sign of temperature gradients, which is contradictory to predictions from hydro dynamical simulations of cluster mergers. Due to the non-symmetric form of the main cluster we extract three surface brightness profiles in different sectors around its centre. We see large variations between the profiles, which we quantify by beta model fitting. The Corresponding r(c)'s vary between 0.1-0.5 Mpc and the beta's between 0.5-1.2. The variations of the profiles and the beta model parameters indicate that the main cluster is not entirely relaxed. This hypothesis is strengthened further by the fact that the cluster is over luminous with respect to the (z-evolving) L-x-T relation found for nearby Clusters.Galaxy Clusters show a high degree of self-similarity. Comparing Our profiles to the scaled reference emission measure profile of Arnaud et al. based on nearby clusters, we find that only the profile extracted north-east (NE) of the main cluster centre is similar to this reference profile. This indicates that only the NE profile is representative for the relaxed part of this cluster component.Based on the beta model parameters of the NE profile and the spectroscopically fitted temperature of kT=4.9(-0.4)(+0.5) keV we find for the total mass within r(500) using the hydrostatic approach M-500similar to 4x10(14) M-circle dot for the main cluster component. This value is in good agreement with the value (M-500=3.9x10(14) M-circle dot) obtained using the z-evolving M-500-T relation from the HIFLUGCS sample based on neat-by clusters. A non-z-evolving M-T relation is only marginally consistent with our result. This is an indication that there exists evolution in the M-T relation, as predicted from simple scaling laws. Calculating the cot-responding gas mass fraction we find f(g)similar to18-20% which is in good agreement with other work. We also develop a simple on-axis merger model for the cluster. As input we use the projected distance of the subcluster to the main cluster centre and the velocity difference of main and subcluster based on four galaxy redshifts spectroscopically measured with the Kitt Peak telescope. Together with a simple ram pressure model we find that the most likely physical distance of the subcluster to the main cluster lies between 0.6<d<1.0 Mpc. The coherent results of on-axis merger and ram pressure model suggest that the merger in this cluster is indeed on-axis and not an off-axis merger with a large impact parameter. We find for the ratio of subcluster to main cluster mass values between 20-30% which indicates that the merger in RX J0256.5+0006 is a major merging event.

We give a general description of the optical observing strategy of the ROSAT-ESO Flux-Limited X-ray (REFLEX) cluster survey. This presently includes 460 clusters of galaxies selected from the ROSAT All-Sky Survey in the Southern hemisphere, to a flux limit of 3 10^-12 erg s^-1 cm^-2. Redshifts are now measured for 95 and then extend the sample to fainter fluxes. A few highlights on the large-scale distribution of REFLEX clusters and their clustering properties are also discussed.

We present here a study of XMM-Newton data of two distant galaxy cluster candidates. One of these was discovered serendipitously in near infrared data, CL J0533-2411, the other one corresponds to the cluster EIS J0533-2412 part of the EIS cluster survey. The estimated redshift of CL J0533-2411 is z = 1.2-1.7. EIS J0533-2412 is a rich system (Lambda(cl) = 299), with a spectroscopically confirmed redshift of z = 1.3. Both galaxy concentrations show firm X-ray detections, located within 30" of their optical center. However, we cannot resolve the sources with XMM-Newton. If the X-ray emission originates from the X-ray emitting intra-cluster medium (ICM) it would be extremely concentrated which is rather unlikely (core radii below 14 h(65)(-1) kpc and 40 h(65)(-1) kpc, respectively). We argue that the X-ray sources are more likely AGN members of the galaxy concentrations. We set an upper limit for the bolometric luminosity of a hot ICM in the range similar to0.7-2.1 x 10(44) h(65)(-2) erg/s for CL J0533-2411, depending on the exact redshift. For EIS J0533-2412 the limit is L-bol = (6.2 +/- 1.4) x 10(43) h(65)(-2) erg/s. We interpret our result in the following way: EIS J0533-2412 (and possibly CL J0533-2411) are proto-clusters and show matter overdensities before collapse, which explains the low significance of extended X-ray emission.

We present the follow-up of three medium redshift galaxy clusters from the SHARC survey observed with XMM-Newton. We studied RX J0256.5+0006 which shows two components which are very likely in interaction. The smallest component exhibits a comet-like structure indicating ram pressure stripping as it falls onto the main cluster. The second cluster, RX J2237.0-1516 is an elliptical cluster with a gas temperature of 3.0$\pm$0.5 keV. The third cluster, RX J1200.8-0328 seems to be in a relaxed state because its shape is regular and we do not see obvious temperature gradient. Its mean temperature is 5.1$^{+0.7}_{-0.5}$ keV.

We present in this paper a substructure and spectroimaging study of the Coma cluster of galaxies based on XMM-Newton data. XMM-Newton performed a mosaic of observations of Coma to ensure a large coverage of the cluster. We add the different pointings together and fit elliptical beta-models to the data. We subtract the cluster models from the data and look for residuals, which can be interpreted as substructure. We find several significant structures: the well-known subgroup connected to NGC 4839 in the South-West of the cluster, and another substructure located between NGC 4839 and the centre of the Coma cluster. Constructing a hardness ratio image, which can be used as a temperature map, we see that in front of this new structure the temperature is significantly increased (higher or equal 10 keV). We interpret this temperature enhancement as the result of heating as this structure falls onto the Coma cluster. We furthermore reconfirm the filament-like structure South-East of the cluster centre. This region is significantly cooler than the mean cluster temperature. We estimate the temperature of this structure to be equal or below 1 keV. A possible scenario to explain the observed features is stripping caused by the infall of a small group of galaxies located around the two galaxies NGC 4921 and NGC 4911 into the Coma cluster with a non-zero impact parameter. We also see significant X-ray depressions North and South-East of NGC 4921, which might either be linked to tidal forces due to the merger with the Western structure or connected to an older cluster merger.

We report on a 20 ks XMM observation of the distant cluster RX J1120.1+4318, discovered at z = 0.6 in the SHARC survey. The cluster has a regular spherical morphology, suggesting it is in a relaxed state. The combined fit of the EPIC/MOS&pn camera gives a cluster mean temperature of kT = 5.3 +/- 0.5 keV with an iron abundance of 0.47 +/- 0.19. The temperature profile, measured for the first time at such a redshift, is consistent with an isothermal atmosphere up to half the virial radius. The surface brightness profile, measured nearly up to the virial radius, is well fitted by a beta-model, with beta = 0.78(-0.04)(+0.06) and a core radius of theta(c) = 0.44(-0.04)(+0.06) arcmin. We compared the properties of RX J1120.1+4318 with the properties of nearby clusters for two cosmological models. an Einstein-de Sitter Universe and a flat low density Universe with Omega(0) = 0.3. For both models, the scaled emission measure profile beyond the core, the gas mass fraction and luminosity are consistent with the expectations of the self-similar model of cluster formation, although a slightly better agreement is obtained for a low density Universe. There is no evidence of a central cooling flow, in spite of the apparent relaxed state of the cluster. This is consistent with its estimated cooling time, larger than the age of the Universe at the cluster redshift. The entropy profile shows a flat core with a central entropy of similar to140 keV cm(2), remarkably similar to the entropy floor observed in nearby clusters, and a rising profile beyond typically 0.1 virial radius. Implications of our results, in terms of non-gravitational physics in cluster formation, are discussed.

We have performed a combined analysis of X-ray and Sunyaev-Zel'dovich data in the direction of the dis- tant galaxy cluster, RX J2228+2037. Fitting a-model to the high-resolution HRI data givesrc = 10312h 1 70 kpc and =0 :54 0:03. The dependency of the Sunyaev-Zel'dovich eect with respect to the gas temperature al- lows us, through the additional use of the 21 GHz data of the cluster, to determine kBTe =1 0:4 1:8h 1=2 70 keV. Extrapolating the gas density prole out to the virial radius (Rv = r178 =2 :9 Mpc), we derived a gas mass of