We present constraints on the mean matter density, Ωm, dark energy density, ΩDE, and the dark energy equation of state parameter, w, using Chandra measurements of the X-ray gas mass fraction (fgas) ...in 42 hot (kT > 5 keV), X-ray luminous, dynamically relaxed galaxy clusters spanning the redshift range 0.05 < z < 1.1. Using only the fgas data for the six lowest redshift clusters at z < 0.15, for which dark energy has a negligible effect on the measurements, we measure Ωm= 0.28 ± 0.06 (68 per cent confidence limits, using standard priors on the Hubble constant, H0, and mean baryon density, Ωb h2). Analysing the data for all 42 clusters, employing only weak priors on H0 and Ωb h2, we obtain a similar result on Ωm and a detection of the effects of dark energy on the distances to the clusters at ∼99.99 per cent confidence, with ΩDE= 0.86 ± 0.21 for a non-flat ΛCDM model. The detection of dark energy is comparable in significance to recent type Ia supernovae (SNIa) studies and represents strong, independent evidence for cosmic acceleration. Systematic scatter remains undetected in the fgas data, despite a weighted mean statistical scatter in the distance measurements of only ∼5 per cent. For a flat cosmology with a constant dark energy equation of state, we measure Ωm= 0.28 ± 0.06 and w=−1.14 ± 0.31. Combining the fgas data with independent constraints from cosmic microwave background and SNIa studies removes the need for priors on Ωb h2 and H0 and leads to tighter constraints: Ωm= 0.253 ± 0.021 and w=−0.98 ± 0.07 for the same constant-w model. Our most general analysis allows the equation of state to evolve with redshift. Marginalizing over possible transition redshifts 0.05 < zt < 1, the combined fgas+ CMB + SNIa data set constrains the dark energy equation of state at late and early times to be w0=−1.05 ± 0.29 and wet=−0.83 ± 0.46, respectively, in agreement with the cosmological constant paradigm. Relaxing the assumption of flatness weakens the constraints on the equation of state by only a factor of ∼2. Our analysis includes conservative allowances for systematic uncertainties associated with instrument calibration, cluster physics and data modelling. The measured small systematic scatter, tight constraint on Ωm and powerful constraints on dark energy from the fgas data bode well for future dark energy studies using the next generation of powerful X-ray observatories, such as Constellation-X.
This is the third in a series of papers studying the astrophysics and cosmology of massive, dynamically relaxed galaxy clusters. Our sample comprises 40 clusters identified as being dynamically ...relaxed and hot (i.e. massive) in Papers I and II of this series. Here we consider the thermodynamics of the intracluster medium, in particular the profiles of density, temperature and related quantities, as well as integrated measurements of gas mass, average temperature, total luminosity and centre-excluded luminosity. We fit power-law scaling relations of each of these quantities as a function of redshift and cluster mass, which can be measured precisely and with minimal bias for these relaxed clusters using hydrostatic arguments. For the thermodynamic profiles, we jointly model the density and temperature and their intrinsic scatter as a function of radius, thus also capturing the behaviour of the gas pressure and entropy. For the integrated quantities, we also jointly fit a multidimensional intrinsic covariance. Our results reinforce the view that simple hydrodynamical models provide a good description of relaxed clusters outside their centres, but that additional heating and cooling processes are important in the inner regions (radii r ... 0.5 r sub( 2500) ... 0.15 r sub( 500)). The thermodynamic profiles remain regular, with small intrinsic scatter, down to the smallest radii where deprojection is straightforward (~20 kpc); within this radius, even the most relaxed systems show clear departures from spherical symmetry. Our results suggest that heating and cooling are continuously regulated in a tight feedback loop, allowing the cluster atmosphere to remain stratified on these scales. (ProQuest: ... denotes formulae/symbols omitted.)
This is the second in a series of papers studying the astrophysics and cosmology of massive, dynamically relaxed galaxy clusters. The data set employed here consists of Chandra observations of 40 ...such clusters, identified in a comprehensive search of the Chandra archive for hot (kT ... 5 keV), massive, morphologically relaxed systems, as well as high-quality weak gravitational lensing data for a subset of these clusters. Here we present cosmological constraints from measurements of the gas mass fraction, ..., for this cluster sample. By incorporating a robust gravitational lensing calibration of the X-ray mass estimates, and restricting our measurements to the most self-similar and accurately measured regions of clusters, we significantly reduce systematic uncertainties compared to previous work. Our data for the first time constrain the intrinsic scatter in fgas, 7.4 ± 2.3 per cent in a spherical shell at radii 0.8-1.2 ... (~1/4 of the virial radius), consistent with the expected level of variation in gas depletion and non-thermal pressure for relaxed clusters. From the lowest redshift data in our sample, five clusters at z < 0.16, we obtain a constraint on a combination of the Hubble parameter and cosmic baryon fraction, ... = 0.089 ± 0.012, that is insensitive to the nature of dark energy. Combining this with standard priors on h and ... provides a tight constraint on the cosmic matter density, ... = 0.27 ± 0.04, which is similarly insensitive to dark energy. Using the entire cluster sample, extending to z > 1, we obtain consistent results for ... and interesting constraints on dark energy: ... for non-flat ...CDM (cosmological constant) models, and w = -0.98 ± 0.26 for flat models with a constant dark energy equation of state. Our results are both competitive and consistent with those from recent cosmic microwave background, Type Ia supernova and baryon acoustic oscillation data. We present constraints on more complex models of evolving dark energy from the combination of fgas data with these external data sets, and comment on the possibilities for improved fgas constraints using current and next-generation X-ray observatories and lensing data. (ProQuest: ... denotes formulae/symbols omitted.)
ABSTRACT
We present constraints on the mean dark energy density, ΩX and dark energy equation of state parameter, wX, based on Chandra measurements of the X‐ray gas mass fraction in 26 X‐ray luminous, ...dynamically relaxed galaxy clusters spanning the redshift range 0.07 < z < 0.9. Under the assumption that the X‐ray gas mass fraction measured within r2500 is constant with redshift and using only weak priors on the Hubble constant and mean baryon density of the Universe, we obtain a clear detection of the effects of dark energy on the distances to the clusters, confirming (at comparable significance) previous results from Type Ia supernovae studies. For a standard Λ cold dark matter (CDM) cosmology with the curvature ΩK included as a free parameter, we find ΩΛ= 0.94+0.21−0.23 (68 per cent confidence limits). We also examine extended XCDM dark energy models. Combining the Chandra data with independent constraints from cosmic microwave background experiments, we find ΩX= 0.75 ± 0.04, Ωm= 0.26+0.06−0.04 and wX=−1.26 ± 0.24. Imposing the prior constraint wX > −1, the same data require wX < −0.7 at 95 per cent confidence. Similar results on the mean matter density and dark energy equation of state parameter, Ωm= 0.24 ± 0.04 and wX=−1.20+0.24−0.28, are obtained by replacing the cosmic microwave background data with standard priors on the Hubble constant and mean baryon density and assuming a flat geometry.
This is the fourth in a series of papers studying the astrophysics and cosmology of massive, dynamically relaxed galaxy clusters. Here, we use measurements of weak gravitational lensing from the ...Weighing the Giants project to calibrate Chandra X-ray measurements of total mass that rely on the assumption of hydrostatic equilibrium. This comparison of X-ray and lensing masses measures the combined bias of X-ray hydrostatic masses from both astrophysical and instrumental sources. While we cannot disentangle the two sources of bias, only the combined bias is relevant for calibrating cosmological measurements using relaxed clusters. Assuming a fixed cosmology, and within a characteristic radius (r
2500) determined from the X-ray data, we measure a lensing to X-ray mass ratio of 0.96 ± 9 per cent (stat) ± 9 per cent (sys). We find no significant trends of this ratio with mass, redshift or the morphological indicators used to select the sample. Our results imply that any departures from hydrostatic equilibrium at these radii are offset by calibration errors of comparable magnitude, with large departures of tens-of-percent unlikely. In addition, we find a mean concentration of the sample measured from lensing data of
$c_{200} = 3.0_{-1.8}^{+4.4}$
. Anticipated short-term improvements in lensing systematics, and a modest expansion of the relaxed lensing sample, can easily increase the measurement precision by 30–50 per cent, leading to similar improvements in cosmological constraints that employ X-ray hydrostatic mass estimates, such as on Ωm from the cluster gas mass fraction.
We use the Chandra X-ray Observatory to study the dark matter haloes of 34 massive, dynamically relaxed galaxy clusters, spanning the redshift range 0.06 < z < 0.7. The observed dark matter and total ...mass (dark-plus-luminous matter) profiles can be approximated by the Navarro–Frenk–White (hereafter NFW) model for cold dark matter (CDM) haloes; for ∼80 per cent of the clusters, the NFW model provides a statistically acceptable fit. In contrast, the singular isothermal sphere model can, in almost every case, be completely ruled out. We observe a well-defined mass–concentration relation for the clusters with an intrinsic scatter in good agreement with the predictions from simulations. The slope of the mass–concentration relation, c∝Mavir/(1 +z)b with a=−0.45 ± 0.12 at 95 per cent confidence, is steeper than the value a∼− 0.1 predicted by CDM simulations for lower mass haloes. With the slope a included as a free fit parameter, the redshift evolution of the concentration parameter, b= 0.71 ± 0.52 at 95 per cent confidence, is consistent with the same simulations (b∼ 1). Fixing a∼−0.1 leads to an apparent evolution that is significantly slower, b= 0.30 ± 0.49, although the goodness of fit in this case is significantly worse. Using a generalized NFW model, we find the inner dark matter density slope, α, to be consistent with unity at 95 per cent confidence for the majority of clusters. Combining the results for all clusters for which the generalized NFW model provides a good description of the data, we measure α= 0.88 ± 0.29 at 95 per cent confidence, in agreement with CDM model predictions.
Acute infections and venous thromboembolism Schmidt, M.; Horvath-Puho, E.; Thomsen, R. W. ...
Journal of internal medicine,
June 2012, Letnik:
271, Številka:
6
Journal Article
Recenzirano
Odprti dostop
. Schmidt M, Horvath‐Puho E, Thomsen RW, Smeeth L, Sørensen HT (Department of Clinical Epidemiology, Institute of Clinical Medicine, Aarhus University Hospital, Aarhus, Denmark; and Department of ...Non‐Communicable Epidemiology, London School of Hygiene and Tropical Medicine, London, UK). Acute infections and venous thromboembolism. J Intern Med 2012; 271: 608–618.
Background. Data on the association between acute infections and venous thromboembolism (VTE) are sparse. We examined whether various hospital‐diagnosed infections or infections treated in the community increase the risk of VTE.
Methods. We conducted this population‐based case–control study in Northern Denmark (population 1.8 million) using medical databases. We identified all patients with a first hospital‐diagnosed VTE during the period 1999–2009 (n = 15 009). For each case, we selected 10 controls from the general population matched for age, gender and county of residence (n = 150 074). We identified all hospital‐diagnosed infections and community prescriptions for antibiotics 1 year predating VTE. We used odds ratios from a conditional logistic regression model to estimate incidence rate ratios (IRRs) of VTE within different time intervals of the first year after infection, controlling for confounding.
Results. Respiratory tract, urinary tract, skin, intra‐abdominal and bacteraemic infections diagnosed in hospital or treated in the community were associated with a greater than equal to twofold increased VTE risk. The association was strongest within the first 2 weeks after infection onset, gradually declining thereafter. Compared with individuals without infection during the year before VTE, the IRR for VTE within the first 3 months after infection was 12.5 (95% confidence interval (CI): 11.3–13.9) for patients with hospital‐diagnosed infection and 4.0 (95% CI: 3.8–4.1) for patients treated with antibiotics in the community. Adjustment for VTE risk factors reduced these IRRs to 3.3 (95% CI: 2.9–3.8) and 2.6 (95% CI: 2.5–2.8), respectively. Similar associations were found for unprovoked VTE and for deep venous thrombosis and pulmonary embolism individually.
Conclusions. Infections are a risk factor for VTE.
We present preliminary results from a deep observation lasting almost 200 ks of the centre of the Perseus cluster of galaxies around NGC 1275. The X-ray surface brightness of the intracluster gas ...beyond the inner 20 kpc, which contains the inner radio bubbles, is very smooth apart from some low-amplitude quasi-periodic ripples. A clear density jump at a radius of 24 kpc to the north-east, about 10 kpc out from the bubble rim, appears to be due to a weak shock driven by the northern radio bubble. A similar front may exist around both inner bubbles but is masked elsewhere by rim emission from bright cooler gas. The continuous blowing of bubbles by the central radio source, leading to the propagation of weak shocks and viscously dissipating sound waves seen as the observed fronts and ripples, gives a rate of working which balances the radiative cooling within the inner 50 kpc of the cluster core.
We present long-term photometric observations of the young open cluster IC 348 with a baseline time-scale of 2.4 yr. Our study was conducted with several telescopes from the Young Exoplanet Transit ...Initiative (YETI) network in the Bessel R band to find periodic variability of young stars. We identified 87 stars in IC 348 to be periodically variable; 33 of them were unreported before. Additionally, we detected 61 periodic non-members of which 41 are new discoveries. Our wide field of view was the key to those numerous newly found variable stars. The distribution of rotation periods in IC 348 has always been of special interest. We investigate it further with our newly detected periods but we cannot find a statistically significant bimodality. We also report the detection of a close eclipsing binary in IC 348 composed of a low-mass stellar component (M ≳ 0.09 M⊙) and a K0 pre-main-sequence star (M ≈ 2.7 M⊙). Furthermore, we discovered three detached binaries among the background stars in our field of view and confirmed the period of a fourth one.
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