The Large Scale X-ray Emission from M87

We describe asymmetrical features in a long exposure X-ray map of M87 made with the ROSAT High Resolution Imager (HRI). A bright triangular region is marked by a linear `spur' along one edge. The structure of this spur suggests an interpretation of a tangential view of a shock front 18 kpc long. None of the brighter features are spatially coincident with radio or optical structures so we concur with earlier investigators that most of the emission arises from thermal processes.Comment: 6 pages latex, including 3 postscript figures. Uses psfig and LAMUPHYS (Springer) macro. To be published in 'The M87 Ringberg Workshop', September 1997, Springer Lecture Notes in Physics Series, Roeser and Meisenheimer, ed

XMM-Newton detection of two clusters of galaxies with strong SPT Sunyaev-Zel'dovich effect signatures

We report on the discovery of two galaxy clusters, SPT-CL J2332-5358 and SPT-CL J2342-5411, in X-rays. These clusters were also independently detected through their Sunyaev-Zel'dovich effect by the South Pole Telescope, and confirmed in the optical band by the Blanco Cosmology Survey. They are thus the first clusters detected under survey conditions by all major cluster search approaches. The X-ray detection is made within the frame of the XMM-BCS cluster survey utilizing a novel XMM-Newton mosaic mode of observations. The present study makes the first scientific use of this operation mode. We estimate the X-ray spectroscopic temperature of SPT-CL J2332-5358 (at redshift z=0.32) to T = 9.3 (+3.3/-1.9) keV, implying a high mass, M_{500} = 8.8 +/- 3.8 \times 10^{14} M_{sun}. For SPT-CL J2342-5411, at z=1.08, the available X-ray data doesn't allow us to directly estimate the temperature with good confidence. However, using our measured luminosity and scaling relations we estimate that T = 4.5 +/- 1.3 keV and M_{500} = 1.9 +/- 0.8 \times 10^{14} M_{sun}. We find a good agreement between the X-ray masses and those estimated from the Sunyaev-Zel'dovich effect.Comment: Submitted to A&A, 8 pages, 5 figures, 1 tabl

The galaxy cluster Ysz-Lx and Ysz-M relations from the WMAP 5-yr data

We use multifrequency matched filters to estimate, in the WMAP 5-year data, the Sunyaev-Zel'dovich (SZ) fluxes of 893 ROSAT NORAS/REFLEX clusters spanning the luminosity range Lx,[0.1-2.4]keV = 2 10^{41} - 3.5 10^{45} erg s^{-1}. The filters are spatially optimised by using the universal pressure profile recently obtained from combining XMM-Newton observations of the REXCESS sample and numerical simulations. Although the clusters are individually only marginally detected, we are able to firmly measure the SZ signal (>10 sigma) when averaging the data in luminosity/mass bins. The comparison between the bin-averaged SZ signal versus luminosity and X-ray model predictions shows excellent agreement, implying that there is no deficit in SZ signal strength relative to expectations from the X-ray properties of clusters. Using the individual cluster SZ flux measurements, we directly constrain the Y500-Lx and Y500-M500 relations, where Y500 is the Compton y-parameter integrated over a sphere of radius r500. The Y500-M500 relation, derived for the first time in such a wide mass range, has a normalisation Y*500=[1.60 pm 0.19] 10^{-3} arcmin^2 at M500=3 10^{14} h^{1} Msun, in excellent agreement with the X-ray prediction of 1.54 10^{-3} arcmin^2, and a mass exponent of alpha=1.79 pm 0.17, consistent with the self-similar expectation of 5/3. Constraints on the redshift exponent are weak due to the limited redshift range of the sample, although they are compatible with self-similar evolution.Comment: Version accepted for publication in Astronomy and Astrophysic

Effects of Selection and Covariance on X-ray Scaling Relations of Galaxy Clusters

We explore how the behavior of galaxy cluster scaling relations are affected by flux-limited selection biases and intrinsic covariance among observable properties. Our models presume log-normal covariance between luminosity (L) and temperature (T) at fixed mass (M), centered on evolving, power-law mean relations as a function of host halo mass. Selection can mimic evolution; the \lm and \lt relations from shallow X-ray flux-limited samples will deviate from mass-limited expectations at nearly all scales while the relations from deep surveys (10^{-14} \cgsflux) become complete, and therefore unbiased, at masses above \sims 2 \times 10^{14} \hinv \msol. We derive expressions for low-order moments of the luminosity distribution at fixed temperature, and show that the slope and scatter of the \lt relation observed in flux-limited samples is sensitive to the assumed \lt correlation coefficient. In addition, \lt covariance affects the redshift behavior of halo counts and mean luminosity in a manner that is nearly degenerate with intrinsic population evolution.Comment: 5pages, 4 Figures, Submitted to MNRA

Introducing BAX: a database for X-ray clusters and groups of galaxies

We present BAX, Base de Donnees Amas de Galaxies X (http://webast.ast.obs-mip.fr/bax), a multi-wavelength database dedicated to X-ray clusters and groups of galaxies allowing detailed information retrieval. BAX is designed to support astronomical research by providing access to published measurements of the main physical quantities and to the related bibliographic references: basic data stored in the database are cluster/group identifiers, equatorial coordinates, redshift, flux, X-ray luminosity (in the ROSAT band) and temperature, and links to additional linked parameters (in X-rays, such as spatial profile parameters, as well as SZ parameters of the hot gas, lensing measurements,and data at other wavelengths, such as optical and radio). The clusters and groups in BAX can be queried by the basic parameters as well as the linked parameters or combinations of these. We expect BAX to become an important tool for the astronomical community. BAX will optimize various aspects of the scientific analysis of X-ray clusters and groups of galaxies, from proposal planning to data collection, interpretation and publication, from both ground based facilities like MEGACAM (CFHT), VIRMOS (VLT) and space missions like XMM-Newton, Chandra and Planck.Comment: Accepted for publication in Astronomy and Astrophysics Journal. Contains 4 pages and 1 figur

Weak lensing analysis of MS 1008-1224 with the VLT

We present a gravitational lensing analysis of the cluster of galaxies MS 1008-1224 (z=0.30), based on very deep observations obtained using the VLT with FORS and ISAAC during the science verification phase. We reconstructed the projected mass distribution from B,V,R,I bands using two different methods independently. The mass maps are remarkably similar, which confirm that the PSF correction worked well. The ISAAC and FORS data were combined to measure the photometric redshifts and constrain the redshift distribution of the lensed sources. The total mass inferred from weak shear is 2.3 10^{14} h^{-1} Mo on large scales, in agreement with the X-ray mass. The measured mass profile is well fit by both Navarro, Frenk and White and isothermal sphere with core radius models although the NFW is slightly better. In the inner regions, the lensing mass is about 2 times higher than the X-ray mass, which supports the view that complex physical processes in the innermost parts of clusters are responsible for the X-ray/lensing mass discrepancy. The central part of the cluster is composed of two mass peaks whose the center of mass is 15 arcsecond north of the cD galaxy. This provides an explanation for the 15 arcsecond offset between the cD and the center of the X-ray map reported elsewhere. The optical, X-ray and the mass distributions show that MS 1008-1224 is composed of many subsystems which are probably undergoing a merger. MS 1008-1224 shows a remarkable case of cluster-cluster lensing. The photometric redshifts show an excess of galaxies located 30 arcseconds south-west of the cD galaxy at a redshift of about 0.9 which is lensed by MS 1008-1224. These results show the importance of getting BVRIJK images silmultenously. The VLT is a unique tool to provide such datasets.Comment: 22 pages, submitted to A&A, paper with `big' figures available at ftp://ftp.cita.utoronto.ca/pub/waerbeke/ms1008paper

XMM-Newton Witness of M86 X-ray Metamorphosis

The environmental influence of cluster media on its member galaxies, known as Butcher--Oemler effect, has recently been subject to revision due to numerous observations of strong morphological transformations occurring outside the cluster virial radii, caused by some unidentified gas removal processes. In this context we present new XMM-Newton observations of M86 group. The unique combination of high spatial and spectral resolution and large field of view of XMM-Newton allows an in-depth investigation of the processes involved in the spectacular disruption of this object. We identify a possible shock with Mach number of ~1.4 in the process of crushing the galaxy in the North-East direction. The latter is ascribed to the presence of a dense X-ray emitting filament, previously revealed in the RASS data. The shock is not associated with other previously identified features of M86 X-ray emission, such as the plume, the north-eastern arm and the southern extension, which are found to have low entropy, similar to the inner 2 kpc of M86. Finally, mere existence of the large scale gas halo around the M86 group, suggests that the disruptions of M86's X-ray halo may be caused by small-scale types of interactions such as galaxy-galaxy collisions.Comment: 11 pages, A&A in pres

A Radio Survey of Seven Southern X-ray Luminous Clusters of Galaxies

The Australia Telescope Compact Array (ATCA) has been used at 1.38 and 2.38 GHz to survey seven southern Abell clusters of galaxies with high X-ray luminosities: A2746, A2837, A3126, A3216, A3230, A3827 and A3836. The clusters have also been surveyed at 0.843 GHz with the Molonglo Observatory Synthesis Telescope (MOST). We have listed a complete 1.38-GHz sample of 149 radio sources within the Abell circles centred on their X-ray centroids. We compare their identification fractions, emitted 1.38-GHz and optical powers, radio spectral indices and radial variation in projected source density with those of the radio-selected samples of Slee et al. (1998). We compare our fractional radio luminosity function with that of the radio-selected samples of Ledlow and Owen (1996) and Slee et al. (1998). Three significant differences are noted between X-ray and radio-selected samples of clusters; (1) the X-ray sample has an excess of flat-spectrum radio sources; (2) the fractional radio luminosity function for the FR I sources in the X-ray selected sample is much steeper, implying that fewer of their cluster galaxies become hosts for the stronger FR I radio galaxies; (3) a complete absence of FR II radio galaxies in the X-ray selected sample. The average excess projected density of radio sources near our cluster centres is approx. 5 times the background source density.Comment: 24 pages, 8 figures, plus 6 figures to be published online only; accepted to appear in MNRA

Radio Bubbles in Clusters

We extend our earlier work on cluster cores with distinct radio bubbles, adding more active bubbles, i.e. those with Ghz radio emission, to our sample, and also investigating ``ghost bubbles,'' i.e. those without GHz radio emission. We have determined k, which is the ratio of the total particle energy to that of the electrons radiating between 10 MHz and 10 GHz. Constraints on the ages of the active bubbles confirm that the ratio of the energy factor, k, to the volume filling factor, f lies within the range 1 < k/f < 1000. In the assumption that there is pressure equilibrium between the radio-emitting plasma and the surrounding thermal X-ray gas, none of the radio lobes has equipartition between the relativistic particles and the magnetic field. A Monte-Carlo simulation of the data led to the conclusion that there are not enough bubbles present in the current sample to be able to determine the shape of the population. An analysis of the ghost bubbles in our sample showed that on the whole they have higher upper limits on k/f than the active bubbles, especially when compared to those in the same cluster. A study of the Brightest 55 cluster sample shows that 17, possibly 20, clusters required some form of heating as they have a short central cooling time, t_cool < 3 Gyr, and a large central temperature drop, T_centre/T_outer< 1/2. Of these between 12 (70 per cent) and 15 (75 per cent), contain bubbles. This indicates that the duty cycle of bubbles is large in such clusters and that they can play a major role in the heating process.Comment: 12 pages, Accepted for publication in MNRA

Extended X-ray emission from radio galaxy cocoons

We study the emission of X-rays from lobes of FR-II radio galaxies by inverse Compton scattering of microwave background photons. Using a simple model that takes into account injection of relativistic electrons, their energy losses through adiabatic expansion, synchrotron and inverse Compton emission, and also the stopping of the jet after a certain time, we study the evolution of the total X-ray power, the surface brightness, angular size of the X-ray bright region and the X-ray photon index, as functions of time and cocoon size, and compare the predictions with observations. We find that the radio power drops rapidly after the stopping of the jet, with a shorter time-scale than the X-ray power. The X-ray spectrum initially hardens until the jet stops because the steepening of electron spectrum is mitigated by the injection of fresh particles, for electrons with $\gamma \ge 10^3$. This happens because of the concurrence of two times scales, that of the typical jet lifetimes and cooling due to inverse Compton scattering ($\sim 10^{7\hbox{--}8}$ yr), of electrons responsible for scattering CMB photons into keV range photons (with $\gamma \sim \sqrt{1 \, {\rm keV}/ kT_{CMB}}$). Another finding is that the ratio of the X-ray to radio power is a robust parameter that varies mostly with redshift and ambient density, but is weakly dependent on other parameters. We also determine the time-averaged ratio of X-ray to radio luminosities (at 1 keV and 151 MHz) and find that it scales with redshift as $\propto (1+z)^{3.8}$, for typical values of parameters. We then estimate the X-ray luminosity function of FR-II radio galaxies and estimate the number of these diffuse X-ray bright objects above a flux limit of $\sim 3 \times 10^{-16}$ erg cm$^{-2}$ s$^{-1}$ to be $\sim 25$ deg$^{-2}$.Comment: 9 pages, 5 figures, accepted for publication in MNRAS (replaced with final version to match the printed version