Browsing by Author "Hornstrup, A"

Now showing 1 - 4 of 4
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    A catalog of 203 galaxy clusters serendipitously detected in the ROSAT PSPC pointed observations
    (1998) Vikhlinin, A; McNamara, BR; Forman, W; Jones, C; Quintana, H; Hornstrup, A
    We present a catalog of 203 clusters of galaxies serendipitously detected in 647 ROSAT PSPC high Galactic latitude pointings covering 158 deg(2). 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 17.'5 of the ROSAT PSPC field of view using the spatial extent of their X-ray emission. Fluxes of detected clusters range from 1.6 x 10(-14) to 8 x 10(-12) ergs s(-1) cm(-2) in the 0.5-2 keV energy band. X-ray luminosities range from 10(42) ergs s(-1), corresponding to very poor groups, to similar to 5 x 10(44) 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 x 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 deg(2) survey by Rosati et al. In particular, at a flux of 2 x 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 similar to 2 sigma 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.
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    Cosmological constraints from the evolution of the cluster baryon mass function at z ∼ 0.5
    (2003) Vikhlinin, A; Voevodkin, A; Mullis, CR; VanSpeybroeck, L; Quintana, H; McNamara, BR; Gioia, I; Hornstrup, A; Henry, JP; Forman, WR; Jones, C
    We present a new method for deriving cosmological constraints based on the evolution of the baryon mass function of galaxy clusters and implement it using 17 distant clusters from our 160 deg(2) ROSAT survey. The method uses the cluster baryon mass as a proxy for the total mass, thereby avoiding the large uncertainties of the M-tot-T or M-tot-L-X relations used in all previous studies. Instead, we rely on a well-founded assumption that the M-b/M-tot ratio is a universal quantity, which should result in a much smaller systematic uncertainty. 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 Omega(m)-Lambda plane, Omega(m) + 0.23Lambda = 0.41 +/- 0.10 at 68% confidence, which intersects with constraints from the cosmic microwave background and Type Ia supernovae near Omega(m) = 0.3 and Lambda = 0.7.
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    Evolution of cluster X-ray luminosities and radii: Results from the 160 square degree rosat survey
    (1998) Vikhlinin, A; McNamara, BR; Forman, W; Jones, C; Quintana, H; Hornstrup, A
    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, L-X > 3 x 10(44) ergs s(-1) in the 0.5-2 keV band. We detect a factor of 3-4 deficit of such luminous clusters at z > 0.3 compared with the present. The evolution is much weaker or absent at modestly lower luminosities, (1-3) x 10(44) ergs s(-1). At still lower luminosities, we find no evolution from the analysis of the log N-log S relation. The results in the two upper L, bins are in agreement with the Einstein Extended Medium-Sensitivity Survey evolution result (Gioia et al.; Henry ct al.), which was obtained using a completely independent cluster sample. The low-L-X results are in agreement with other ROSAT surveys (e.g., Rosati et al.; Jones et al.). We also compare the distribution of core radii of nearby and distant (z > 0.4) luminous (with equivalent temperatures of 4-7 keV) clusters and detect no evolution. The ratio of average core radius for z similar to 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 a high-Omega universe.
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    The 160 Square Degree ROSAT Survey
    (2003) Mullis, CR; McNamara, BR; Quintana, H; Vikhlinin, A; Henry, JP; Gioia, IM; Hornstrup, A; Forman, W; Jones, C
    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 z(median) = 0.25, and the median X-ray luminosity is L-X,L-median = 4.2 x 10(43) h(50)(-2) 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 x 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.