Calibration of the Mass-Temperature Relation for Clusters of Galaxies Using Weak Gravitational Lensing

The main uncertainty in current determinations of the power spectrum normalization, sigma_8, from abundances of X-ray luminous galaxy clusters arises from the calibration of the mass-temperature relation. We use our weak lensing mass determinations of 30 clusters from the hitherto largest sample of clusters with lensing masses, combined with X-ray temperature data from the literature, to calibrate the normalization of this relation at a temperature of 8 keV, M_{500c,8 keV}=(8.7 +/- 1.6) h^{-1} 10^{14} M_sun. This normalization is consistent with previous lensing-based results based on smaller cluster samples, and with some predictions from numerical simulations, but higher than most normalizations based on X-ray derived cluster masses. Assuming the theoretically expected slope alpha=3/2 of the mass-temperature relation, we derive sigma_8 = 0.88 +/-0.09 for a spatially-flat LambdaCDM universe with Omega_m = 0.3. The main systematic errors on the lensing masses result from extrapolating the cluster masses beyond the field-of-view used for the gravitational lensing measurements, and from the separation of cluster/background galaxies, contributing each with a scatter of 20%. Taking this into account, there is still significant intrinsic scatter in the mass-temperature relation indicating that this relation may not be very tight, at least at the high mass end. Furthermore, we find that dynamically relaxed clusters are 75 +/-40% hotter than non-relaxed clusters.Comment: 8 pages, 4 figures, revised version submitted to Ap

A Puzzling Merger in A3266: the Hydrodynamic Picture from XMM-Newton

Using the mosaic of nine XMM-Newton observations, we study the hydrodynamic state of the merging cluster of galaxies Abell 3266. The high quality of the spectroscopic data and large field of view of XMM-Netwon allow us to determine the thermodynamic conditions of the intracluster medium on scales of order of 50 kpc. A high quality entropy map reveals the presence of an extended region of low entropy gas, running from the primary cluster core toward the northeast along the nominal merger axis. The mass of the low entropy gas amounts to approximately 2e13 solar masses, which is comparable to the baryonic mass of the core of a rich cluster. We test the possibility that the origin of the observed low entropy gas is either related to the disruption a preexisting cooling core in Abell 3266 or to the stripping of gas from an infalling subcluster companion. We find that both the radial pressure and entropy profiles as well as the iron abundance of Abell 3266 do not resemble those in other known cooling core clusters (Abell 478). Thus we conclude that the low entropy region is subcluster gas in the process of being stripped off from its dark matter halo. In this scenario the subcluster would be falling onto the core of A3266 from the foreground. This would also help interpret the observed high velocity dispersion of the galaxies in the cluster center, provided that the mass of the subcluster is at most a tenth of the mass of the main cluster.Comment: 6 pages, ApJ sub

The North Ecliptic Pole Supercluster

We have used the ROSAT All-Sky Survey to detect a known supercluster at z=0.087 in the North Ecliptic Pole region. The X-ray data greatly improve our understanding of this supercluster's characteristics, approximately doubling our knowledge of the structure's spatial extent and tripling the cluster/group membership compared to the optical discovery data. The supercluster is a rich structure consisting of at least 21 galaxy clusters and groups, 12 AGN, 61 IRAS galaxies, and various other objects. A majority of these components were discovered with the X-ray data, but the supercluster is also robustly detected in optical, IR, and UV wavebands. Extending 129 x 102 x 67 (1/h50 Mpc)^3, the North Ecliptic Pole Supercluster has a flattened shape oriented nearly edge-on to our line-of-sight. Owing to the softness of the ROSAT X-ray passband and the deep exposure over a large solid angle, we have detected for the first time a significant population of X-ray emitting galaxy groups in a supercluster. These results demonstrate the effectiveness of X-ray observations with contiguous coverage for studying structure in the Universe.Comment: Accepted for publication in The Astrophysical Journal; 5 pages with 2 embedded figures; uses emulateapj.sty; For associated animations, see http://www.ifa.hawaii.edu/~mullis/nep3d.html; A high-resolution color postscript version of the full paper is available at http://www.ifa.hawaii.edu/~mullis/papers/nepsc.ps.g

Group-cluster merging and the formation of starburst galaxies

A significant fraction of clusters of galaxies are observed to have substructure, which implies that merging between clusters and subclusters is a rather common physical process of cluster formation. It still remains unclear how cluster merging affects the evolution of cluster member galaxies. We report the results of numerical simulations, which show the dynamical evolution of a gas-rich late-type spiral in a merger between a small group of galaxies and a cluster. The simulations demonstrate that time-dependent tidal gravitational field of the merging excites non-axisymmetric structure of the galaxy, subsequently drives efficient transfer of gas to the central region, and finally triggers a secondary starburst. This result provides not only a new mechanism of starbursts but also a close physical relationship between the emergence of starburst galaxies and the formation of substructure in clusters. We accordingly interpret post-starburst galaxies located near substructure of the Coma cluster as one observational example indicating the global tidal effects of group-cluster merging. Our numerical results furthermore suggest a causal link between the observed excess of blue galaxies in distant clusters and cluster virialization process through hierarchical merging of subclusters.Comment: 5 pages 3 color figures, ApJL in pres

The ROSAT North Ecliptic Pole Survey: The Optical Identifications

The X-ray data around the North Ecliptic Pole (NEP) of the ROSAT All Sky Survey have been used to construct a contiguous area survey consisting of a sample of 445 individual X-ray sources above a flux of ~2x10^-14 erg cm^-2 s^-1 in the 0.5-2.0 keV energy band. The NEP survey is centered at RA (2000) = 18h 00m, DEC(2000) = +66deg 33arcmin and covers a region of 80.7 sq. deg at a moderate Galactic latitude of b = 29.8deg. Hence, the NEP survey is as deep and covers a comparable solid angle to the ROSAT serendipitous surveys, but is also contiguous. We have identified 99.6% of the sources and determined redshifts for the extragalactic objects. In this paper we present the optical identifications of the NEP catalog of X-ray sources including basic X-ray data and properties of the sources. We also describe with some detail the optical identification procedure. The classification of the optical counterparts to the NEP sources is very similar to that of previous surveys, in particular the Einstein Extended Medium Sensitivity Survey (EMSS). The main constituents of the catalog are active galactic nuclei (~49%), either type 1 or type 2 according to the broadness of their permitted emission lines. Stellar counterparts are the second most common identification class (~34%). Clusters and groups of galaxies comprise 14%, and BL Lacertae objects 2%. One non-AGN galaxy, and one planetary nebula have also been found. The NEP catalog of X-ray sources is a homogeneous sample of astronomical objects featuring complete optical identification.Comment: Accepted for publication in the ApJS; 33 pages including 12 postscript figures and 3 tables; uses emulateapj.sty. On-line source catalog at http://www.eso.org/~cmullis/research/nep-catalog.htm

Adverse events associated with individual statin treatments for cardiovascular disease: an indirect comparison meta-analysis

Background: Statins are the most widely prescribed drug available. Due to this reason, it is important to understand the risks involved with the drug class and individual statins. Aim: We conducted a meta-analysis and employed indirect comparisons to identify differing risk effects across statins. Design: We included any randomized clinical trial (RCT) of atorvastatin, fluvastatin, lovastatin, pitavastatin, pravastatin, rosuvastatin and simvastatin used for cardiovascular disease event prevention. The main outcome was adverse events [all-cause mortality, cancers, rhabdomylosis, diabetes, aspartate and alanine aminotransferase (AST/ALT), and creatinine kinase (CK) increases beyond the upper limit of normal]. In order to evaluate the relative effects of each drug on adverse events, we calculated adjusted indirect comparisons of the adverse-event outcomes. Results: Seventy-two trials involving 159 458 patients met our inclusion criteria. Overall, statin treatments significantly increased the rate of diabetes when compared to controls (OR: 1.09; 95% CI: 1.02-1.16) and elevated AST (OR: 1.31; 95% CI: 1.04-1.66) and ALT (OR: 1.28; 95% CI: 1.11-1.48) levels when compared to controls. Using indirect comparisons, we also found that atorvastatin significantly elevated AST levels compared to pravastatin (OR: 2.21; 95% CI: 1.13-4.29) and simvastatin significantly increased CK levels when compared to rosuvastatin (OR: 4.39; 95% CI: 1.01-19.07). Higher dose studies had increased risk of AST elevations. Discussion: Although statins are generally well tolerated, there are risks associated with almost all drugs. With few exceptions, statins appear to exert a similar risk across individual drug

Gravitational lensing statistical properties in general FRW cosmologies with dark energy component(s): analytic results

Various astronomical observations have been consistently making a strong case for the existence of a component of dark energy with negative pressure in the universe. It is now necessary to take the dark energy component(s) into account in gravitational lensing statistics and other cosmological tests. By using the comoving distance we derive analytic but simple expressions for the optical depth of multiple image, the expected value of image separation and the probability distribution of image separation caused by an assemble of singular isothermal spheres in general FRW cosmological models with dark energy component(s). We also present the kinematical and dynamical properties of these kinds of cosmological models and calculate the age of the universe and the distance measures, which are often used in classical cosmological tests. In some cases we are able to give formulae that are simpler than those found elsewhere in the literature, which could make the cosmological tests for dark energy component(s) more convenient.Comment: 14 pages, no figure, Latex fil

XMM-Newton observations of the Coma cluster relic 1253+275

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. Both imaging and spectral analysis are performed, and the X-ray emission is compared with the radio emission. 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 from a possible shock in the region of the Coma relic. We therefore suggest that the main 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 10e-13 erg/cm^2 s, 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 microG.Comment: 4 pages, 2 figures, Accepted for publication in A&A Letter