H. Böhringer

The Mass Function of an X-Ray Flux-limited Sample of Galaxy Clusters

A new X-ray-selected and X-ray flux-limited galaxy cluster sample is presented. Based on the ROSAT All-Sky Survey, the 63 brightest clusters with galactic latitude |bII| ? 20? and flux fX(0.1-2.4keV) ? 2 ? 10-11ergss-1cm-2 have been compiled. Gravitational masses have been determined utilizing intracluster gas density profiles, derived mainly from ROSAT PSPC pointed observations, and gas temperatures, as published mainly from ASCA observations, assuming hydrostatic equilibrium. This sample and an extended sample of 106 galaxy clusters is used to establish the X-ray luminosity-gravitational mass relation. From the complete sample the galaxy cluster mass function is determined and used to constrain the mean cosmic matter density and the amplitude of mass fluctuations. Comparison to Press-Schechter type model mass functions in the framework of cold dark matter cosmological models and a Harrison-Zeldovich initial density fluctuation spectrum yields the constraints ?m = 0.12 and ?8 = 0.96 (90% c.l.). Various possible systematic uncertainties are quantified. Adding all identified systematic uncertainties to the statistical uncertainty in a worst-case fashion results in an upper limit ?m < 0.31. For comparison to previous results a relation ?8 = 0.43? is derived. The mass function is integrated to show that the contribution of mass bound within virialized cluster regions to the total matter density is small; i.e., ?cluster = 0.012 for cluster masses larger than 6.4 ? 1013 h M?.

Properties of the X-ray-brightest Abell-type clusters of galaxies (XBACs) from ROSAT All-Sky Survey data — I. The sample

We present an essentially complete, all-sky, X-ray flux limi ted sample of 242 Abell clusters of galaxies (six of which are double) compiled from ROSAT All-Sky Survey data. Our sample is uncontaminated in the sense that systems featuring prominent X-ray point sources such as AGN or foreground stars have been removed. The sample is limited to high Galactic latitudes (jbj� 20 � ), the nominal redshift range of the ACO catalogue of z � 0:2, and X-ray fluxes above 5:0�10 12 erg cm 2 s 1 in the 0.1 ‐ 2.4 keV band. Due to the X-ray flux limit, our sample consists, at intermediate and high redshifts, ex clusively of very X-ray luminous clusters. Since the latter tend to be also optically rich, th e sample is not affected by the optical selection effects and in particular not by the volume incompleteness known to be present in the Abell and ACO catalogues for richness class 0 and 1 clusters. Our sample is the largest X-ray flux limited sample of galaxy c lusters compiled to date and will allow investigations of unprecedented statistica l quality into the properties and distribution of rich clusters in the local Universe.

Galaxy cluster X-ray luminosity scaling relations from a representative local sample (REXCESS)

We examine the X-ray luminosity scaling relations of 31 nearby galaxy clusters from the Representative XMM-Newton Cluster Structure Survey (REXCESS). The objects are selected only in X-ray luminosity, optimally sampling the cluster luminosity function. Temperatures range from 2 to 9 keV, and there is no bias toward any particular morphological type. To reduce measurement scatter we extract pertinent values in an aperture corresponding to R500, estimated using the tight correlation between YX (the product of gas mass and temperature) and total mass. The data exhibit power law relations between bolometric X-ray luminosity and temperature, YX and total mass, all with slopes that are significantly steeper than self-similar expectations. We examine the possible causes for the steepening, finding that structural variations have little effect and that the primary driver appears to be a systematic variation of the gas content with mass. Scatter about the relations is dominated in all cases by the presence of cool cores. The natural logarithmic scatter about the raw X-ray luminosity-temperature relation is about 70 per cent, and about the X-ray luminosity-YX relation it is 40 per cent. Systems with more morphological substructure show similar scatter about scaling relations than clusters with less substructure, due to the preponderance of cool core systems in the regular cluster subsample. Cool core and morphologically disturbed systems occupy distinct regions in the residual space with respect to the best fitting mean relation, the former lying systematically at the high luminosity side, the latter lying systematically at the low luminosity side. Simple exclusion of the central regions serves to reduce the scatter about the scaling relations by more than a factor of two. The scatter reduces by a similar amount with the use of the central gas density as a third parameter. Using YX as a total mass proxy, we derive a Malmquist bias-corrected local luminosity-mass relation and compare with other recent determinations. Our results indicate that luminosity can be a reliable mass proxy with controllable scatter, which has important implications for upcoming all-sky cluster surveys, such as those to be undertaken with Planck and eROSITA ,a nd ultimately for the use of the cluster population for cosmological purposes.

The Northern ROSAT All-Sky (NORAS) Galaxy Cluster Survey. I. X-Ray Properties of Clusters Detected as Extended X-Ray Sources*

In the construction of an X-ray-selected sample of galaxy clusters for cosmological studies, we have assembled a sample of 495 X-ray sources found to show extended X-ray emission in the first processing of the ROSAT All-Sky Survey. The sample covers the celestial region with declination ? ? 0? and Galactic latitude |bII| ? 20? and comprises sources with a count rate ?0.06 counts s-1 and a source extent likelihood of L ? 7. In an optical follow-up identification program we find 378 (76%) of these sources to be clusters of galaxies.?????It was necessary to reanalyze the sources in this sample with a new X-ray source characterization technique to provide more precise values for the X-ray flux and source extent than obtained from the standard processing. This new method, termed growth curve analysis (GCA), has the advantage over previous methods in its ability to be robust, to be easy to model and to integrate into simulations, to provide diagnostic plots for visual inspection, and to make extensive use of the X-ray data. The source parameters obtained assist the source identification and provide more precise X-ray fluxes. This reanalysis is based on data from the more recent second processing of the ROSAT Survey. We present a catalog of the cluster sources with the X-ray properties obtained as well as a list of the previously flagged extended sources that are found to have a noncluster counterpart. We discuss the process of source identification from the combination of optical and X-ray data.?????To investigate the overall completeness of the cluster sample as a function of the X-ray flux limit, we extend the search for X-ray cluster sources to the data of the second processing of the ROSAT Survey for the northern sky region between 9h and 14h in right ascension. We include the search for X-ray emission of known clusters as well as a new investigation of extended X-ray sources. In the course of this search we find X-ray emission from 85 additional Abell clusters and 56 very probable cluster candidates among the newly found extended sources. A comparison of the X-ray cluster number counts of the NORAS sample with the ROSAT-ESO Flux-limited X-Ray (REFLEX) Cluster Survey results leads to an estimate of the completeness of the NORAS sample of ROSAT All-Sky Survey (RASS) I extended clusters of about 50% at an X-ray flux of FX(0.1-2.4 keV) = 3 ? 10-12 ergs s-1 cm-2. The estimated completeness achieved by adding the supplementary sample in the study area amounts to about 82% in comparison to REFLEX. The low completeness introduces an uncertainty in the use of the sample for cosmological statistical studies that will be cured with the completion of the continuing Northern ROSAT All-Sky (NORAS) Cluster Survey project.

Details of the mass-temperature relation for clusters of galaxies

We present results on the total mass and temperature determination using two samples of clusters of galaxies. One sample is constructed with emphasis on the completeness of the sample, while the advantage of the other is the use of the temperature profiles, derived with ASCA. We obtain remarkably similar fits to the

Cooling flows as a calorimeter of active galactic nucleus mechanical power

M-T

A ROSAT survey of Hickson's compact galaxy groups

relation for both samples, with the normalization and the slope significantly different from both prediction of self-similar collapse and hydrodynamical simulations. We discuss the origin of these discrepancies and also combine the X-ray mass with velocity dispersion measurements to provide a comparison with high-resolution dark matter simulations. Finally, we discuss the importance of a cluster formation epoch in the observed

Gas entropy in a representative sample of nearby X-ray galaxy clusters (REXCESS): Relationship to gas mass fraction

M-T

The XMM-Newton wide-field survey in the COSMOS field - The point-like X-ray source catalogue

relation.

The XMM-Newton Wide-Field Survey in the COSMOS Field: Statistical Properties of Clusters of Galaxies

The assumption that radiative cooling of gas in the centers of galaxy clusters is approximately balanced by energy input from a central supermassive black hole implies that the observed X-ray luminosity of the cooling flow region sets a lower limit on AGN mechanical power. The conversion efficiency of AGN mechanical power into gas heating is uncertain, but we argue that it can be high even in the absence of strong shocks. These arguments inevitably lead to the conclusion that the time averaged mechanical power of AGNs in cooling flows is much higher than the presently observed bolometric luminosity of these objects. The energy balance between cooling losses and AGN mechanical power requires some feedback mechanism. We consider a toy model in which the accretion rate onto a black hole is set by the classic Bondi formula. Application of this model to the best studied case of M87 suggests that accretion proceeds at approximately the Bondi rate down to a few gravitational radii with most of the power (at the level of a few percent of the rest mass) carried away by an outflow.