Allan Hornstrup

Chandra Cluster Cosmology Project. II. Samples and X-Ray Data Reduction

We discuss the measurements of the galaxy cluster mass functions at z 0.05 and z 0.5 using high-quality Chandra observations of samples derived from the ROSAT PSPC All-Sky and 400 deg2 surveys. We provide a full reference for the data analysis procedures, present updated calibration of relations between the total cluster mass and its X-ray indicators (TX , M gas, and YX ) based on a subsample of low-z relaxed clusters, and present a first measurement of the evolving LX -M tot relation (with M tot estimated from YX ) obtained from a well defined statistically complete cluster sample and with appropriate corrections for the Malmquist bias applied. Finally, we present the derived cluster mass functions, estimate the systematic uncertainties in this measurement, and discuss the calculation of the likelihood function. We confidently measure the evolution in the cluster comoving number density at a fixed mass threshold, e.g., by a factor of 5.0 ? 1.2 at M 500 = 2.5 ? 1014 h ?1 M ? between z = 0 and 0.5. This evolution reflects the growth of density perturbations, and can be used for the cosmological constraints complementing those from the distance-redshift relation.

JEM-X: The X-ray monitor aboard INTEGRAL ?

The JEM-X monitor provides X-ray spectra and imaging with arcminute angular resolution in the 3 to 35 keV band. The good angular resolution and the low energy response of JEM-X plays an important role in the identification of gamma ray sources and in the analysis and scientific interpretation of the combined X-ray and gamma ray data. JEM-X is a coded aperture instrument consisting of two identical, coaligned telescopes. Each of the detectors has a sensitive area of 500 cm 2 , and views the sky through its own coded aperture mask. The two coded masks are inverted with respect to each other and provides an angular resolution of 3 0 across an eective field of view of about 10 diameter.

A Catalog of 203 Galaxy Clusters Serendipitously Detected in the ROSAT PSPC Pointed Observations

We present a catalog of 203 clusters of galaxies serendipitously detected in 647 ROSAT PSPC high Galactic latitude pointings covering 158 deg2. This is one of the largest X-ray-selected cluster samples, comparable in size only to the ROSAT All-Sky Survey sample of nearby clusters (Ebeling et al. 1997). We detect clusters in the inner 175 of the ROSAT PSPC field of view using the spatial extent of their X-ray emission. Fluxes of detected clusters range from 1.6 × 10-14 to 8 × 10-12 ergs s-1 cm-2 in the 0.5-2 keV energy band. X-ray luminosities range from 1042 ergs s-1, corresponding to very poor groups, to ~5 × 1044 ergs s-1, corresponding to rich clusters. The cluster redshifts range from z = 0.015 to z > 0.5. The catalog lists X-ray fluxes, core radii, and spectroscopic redshifts for 73 clusters and photometric redshifts for the remainder. Our detection method, optimized for finding extended sources in the presence of source confusion, is described in detail. Selection effects necessary for a statistical analysis of the cluster sample are comprehensively studied by Monte Carlo simulations. We have optically confirmed 203 of 223 X-ray sources as clusters of galaxies. Of the remaining 20 sources, 19 are likely false detections arising from blends of unresolved point X-ray sources. Optical identifications of the remaining object are hampered by a bright nearby star. Above a flux of 2 × 10-13 ergs s-1 cm-2, 98% of extended X-ray sources are optically confirmed clusters. The number of false detections and their flux distribution are in perfect agreement with simulations. The log N-log S relation for clusters derived from our catalog shows excellent agreement with counts of bright clusters derived from the Einstein Extended Medium Sensitivity Survey and ROSAT All-Sky Survey. At fainter fluxes, our log N-log S relation agrees with the smaller area WARPS survey. Our cluster counts appear to be systematically higher than those from a 50 deg2 survey by Rosati et al. In particular, at a flux of 2 × 10-13 ergs s-1 cm-2, we find a surface density of clusters of 0.57 ± 0.07 deg-2, which is a factor of 1.3 more than was found by Rosati et al. This difference is marginally significant at the ~2 σ level. The large area of our survey makes it possible to study the evolution of the X-ray luminosity function in the high luminosity range inaccessible with other, smaller area ROSAT surveys.

X-Ray Overluminous Elliptical Galaxies: A New Class of Mass Concentrations in the Universe?

We detect four isolated, X-ray overluminous [Lx > 2 × 1043 -2 ergs s-1] elliptical galaxies (OLEGs) in our 160 deg2 ROSAT PSPC survey. The extent of their X-ray emission, total X-ray luminosity, total mass, and mass of the hot gas in these systems corresponds to poor clusters, and the optical luminosity of the central galaxies (MR 7 keV clusters.

The 160 Square Degree ROSAT Survey: The revised catalog of 201 clusters with spectroscopic redshifts

We present the revised catalog of galaxy clusters detected as extended X-ray sources in the 160 Square Degree ROSAT Survey, including spectroscopic redshifts and X-ray luminosities for 200 of the 201 members. The median redshift is zmedian = 0.25, and the median X-ray luminosity is LX,median = 4.2 × 1043 h ergs s-1 (0.5-2.0 keV). This is the largest high-redshift sample of X-ray-selected clusters published to date. There are 73 objects at z > 0.3 and 22 objects at z > 0.5 drawn from a statistically complete flux-limited survey with a median object flux of 1.4 × 10-13 ergs cm-2 s-1. We describe the optical follow-up of these clusters with an emphasis on our spectroscopy, which has yielded 155 cluster redshifts, 110 of which are presented here for the first time. These measurements, combined with 45 from the literature and other sources, provide near-complete spectroscopic coverage for our survey. We discuss the final optical identifications for the extended X-ray sources in the survey region and compare our results to similar X-ray cluster searches.

Cosmological Constraints from the Evolution of the Cluster Baryon Mass Function

We determine the evolution of the number density of the galaxy clusters between z=0 and z=0.5. Our method uses the cluster baryon mass as a proxy for the total mass, thereby avoiding any uncertainties of the M tot−T or M tot−L X relations. Instead, we rely on a well-founded assumption that the M b /M tot ratio is a universal quantity. Taking advantage of direct and accurate Chandra measurements of the gas masses for distant clusters, we find strong evolution of the baryon mass function between z>0.4 and the present. The observed evolution defines a narrow band in the Ωm−Λ plane which intersects with constraints from the Cosmic Microwave Background and supernovae Ia near Ωm=0.3 and Λ=0.7. Assuming the flat Universe, cluster evolution favors the values of the dark energy equation of state parameter, w≈−1.

Evolution of Cluster X-Ray Luminosities and Radii: Results from the 160 Square Degree ROSAT Survey

We searched for cluster X-ray luminosity and radius evolution using our sample of 200 galaxy clusters detected in the 160 deg^2 survey with the ROSAT PSPC (Vikhlinin et al. 1998, astro-ph/9803099). With such a large area survey, it is possible, for the first time with ROSAT, to test the evolution of luminous clusters, Lx>3x10^44 erg/s, in the 0.5-2 keV band. We detect a factor of 3-4 deficit of such luminous clusters at z>0.3 compared to the present. The evolution is much weaker or absent at modestly lower luminosities, 1-3x10^44 erg/s. At still lower luminosities, we find no evolution from the analysis of the log N - log S relation. The results in the two upper Lx bins are in agreement with the Einstein EMSS evolution result (Gioia et al. 1990a, Henry et al. 1992) while being obtained using a completely independent cluster sample. The low-Lx results are in agreement with other ROSAT surveys (e.g. Rosati et al. 1998, Jones et al. 1998). We also compare the distribution of core radii of nearby and distant (z>0.4) luminous (with equivalent temperatures 4-7 keV) clusters, and detect no evolution. The ratio of average core radius for z~0.5 and z<0.1 clusters is 0.9+/-0.1, and the core radius distributions are remarkably similar. A decrease of cluster sizes incompatible with our data is predicted by self-similar evolution models for high-Omega universe.We searched for cluster X-ray luminosity and radius evolution using our sample of 203 galaxy clusters detected in the 160 deg -->2 survey with the ROSAT PSPC (Vikhlinin et al.). With such a large area survey, it is possible, for the first time with ROSAT, to test the evolution of luminous clusters, LX

ESO 3060170: A MASSIVE FOSSIL GALAXY GROUP WITH A HEATED GAS CORE?

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CHANDRA observations of the NGC 1550 galaxy group: Implication for the temperature and entropy profiles of 1 keV galaxy groups

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Graded d-spacing multilayer telescope for high-energy x-ray astronomy

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