Abstract
Suzaku measurements of a homogeneous metal distribution of Z ∼ 0.3 Solar in the outskirts of the nearby Perseus cluster suggest that chemical elements were deposited and mixed into the ...intergalactic medium before clusters formed, likely over 10 billion years ago. A key prediction of this early enrichment scenario is that the intracluster medium in all massive clusters should be uniformly enriched to a similar level. Here, we confirm this prediction by determining the iron abundances in the outskirts (r > 0.25r
200) of a sample of 10 other nearby galaxy clusters observed with Suzaku for which robust measurements based on the Fe-K lines can be made. Across our sample, the iron abundances are consistent with a constant value, Z
Fe = 0.316 ± 0.012 Solar (χ2 = 28.85 for 25 degrees of freedom). This is remarkably similar to the measurements for the Perseus cluster of Z
Fe = 0.314 ± 0.012 Solar, using the Solar abundance scale of Asplund et al.
Abstract
We present results from Suzaku Key Project observations of the Virgo Cluster, the nearest galaxy cluster to us, mapping its X-ray properties along four long ‘arms’ extending beyond the ...virial radius. The entropy profiles along all four azimuths increase with radius, then level out beyond ∼0.5r200, while the average pressure at large radii exceeds Planck Sunyaev–Zel'dovich measurements. These results can be explained by enhanced gas density fluctuations (clumping) in the cluster's outskirts. Using a standard Navarro, Frenk and White model, we estimate a virial mass, radius and concentration parameter of M200 = 1.05 ± 0.02 × 1014 M⊙, r200 = 974.1 ± 5.7 kpc and c = 8.8 ± 0.2, respectively. The inferred cumulative baryon fraction exceeds the cosmic mean at r ∼ r200 along the major axis, suggesting enhanced gas clumping possibly sourced by a candidate large-scale structure filament along the north–south direction. The Suzaku data reveal a large-scale sloshing pattern, with two new cold fronts detected at radii of 233 and 280 kpc along the western and southern arms, respectively. Two high-temperature regions are also identified 1 Mpc towards the south and 605 kpc towards the west of M87, likely representing shocks associated with the ongoing cluster growth. Although systematic uncertainties in measuring the metallicity for low-temperature plasma remain, the data at large radii appear consistent with a uniform metal distribution on scales of ∼90 × 180 kpc and larger, providing additional support for the early chemical enrichment scenario driven by galactic winds at redshifts of 2–3.
This is the first of a series of papers in which we derive simultaneous constraints on cosmological parameters and X-ray scaling relations using observations of the growth of massive, X-ray ...flux-selected galaxy clusters. Our data set consists of 238 cluster detections from the ROSAT All-Sky Survey, and incorporates follow-up observations of 94 of those clusters using the Chandra X-ray Observatory or ROSAT. Here we describe and implement a new statistical framework required to self-consistently produce simultaneous constraints on cosmology and scaling relations from such data, and present results on models of dark energy. In spatially flat models with a constant dark energy equation of state, w, the cluster data yield Ωm= 0.23 ± 0.04, σ8= 0.82 ± 0.05 and w=−1.01 ± 0.20, incorporating standard priors on the Hubble parameter and mean baryon density of the Universe, and marginalizing over conservative allowances for systematic uncertainties. These constraints agree well and are competitive with independent data in the form of cosmic microwave background anisotropies, type Ia supernovae, cluster gas mass fractions, baryon acoustic oscillations, galaxy redshift surveys and cosmic shear. The combination of our data with current microwave background, supernova, gas mass fraction and baryon acoustic oscillation data yields Ωm= 0.27 ± 0.02, σ8= 0.79 ± 0.03 and w=−0.96 ± 0.06 for flat, constant w models. The combined data also allow us to investigate evolving w models. Marginalizing over transition redshifts in the range 0.05–1, we constrain the equation of state at late and early times to be respectively w0=−0.88 ± 0.21 and wet=−1.05+0.20−0.36, again including conservative systematic allowances. The combined data provide constraints equivalent to a Dark Energy Task Force figure of merit of 15.5. Our results highlight the power of X-ray studies, which enable the straightforward production of large, complete and pure cluster samples and admit tight scaling relations, to constrain cosmology. However, the new statistical framework we apply to this task is equally applicable to cluster studies at other wavelengths.
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.)
We present the results of a Chandra X-ray survey of the eight most massive galaxy clusters at z > 1.2 in the South Pole Telescope 2500 deg2 survey. We combine this sample with previously published ...Chandra observations of 49 massive X-ray-selected clusters at 0 < z < 0.1 and 90 Sunyaev-Zel'dovich-selected clusters at 0.25 < z < 1.2 to constrain the evolution of the intracluster medium (ICM) over the past ∼10 Gyr. We find that the bulk of the ICM has evolved self-similarly over the full redshift range probed here, with the ICM density at scaling like . In the centers of clusters ( ), we find significant deviations from self-similarity ( ), consistent with no redshift dependence. When we isolate clusters with overdense cores (i.e., cool cores), we find that the average overdensity profile has not evolved with redshift-that is, cool cores have not changed in size, density, or total mass over the past ∼9-10 Gyr. We show that the evolving "cuspiness" of clusters in the X-ray, reported by several previous studies, can be understood in the context of a cool core with fixed properties embedded in a self-similarly evolving cluster. We find no measurable evolution in the X-ray morphology of massive clusters, seemingly in tension with the rapidly rising (with redshift) rate of major mergers predicted by cosmological simulations. We show that these two results can be brought into agreement if we assume that the relaxation time after a merger is proportional to the crossing time, since the latter is proportional to .
This is the second in a series of papers in which we derive simultaneous constraints on cosmology and X-ray scaling relations using observations of massive, X-ray flux-selected galaxy clusters. The ...data set consists of 238 clusters with 0.1–2.4 keV luminosities >2.5 × 1044 h−270 erg s−1, and incorporates follow-up observations of 94 of those clusters using the Chandra X-ray Observatory or ROSAT (11 were observed with both). The clusters are drawn from three samples based on the ROSAT All-Sky Survey: the ROSAT Brightest Cluster Sample (78/37 clusters detected/followed-up), the ROSAT-ESO Flux-Limited X-ray sample (126/25) and the bright sub-sample of the Massive Cluster Survey (34/32). Our analysis accounts self-consistently for all selection effects, covariances and systematic uncertainties. Here we describe the reduction of the follow-up X-ray observations, present results on the cluster scaling relations, and discuss their implications. Our constraints on the luminosity–mass and temperature–mass relations, measured within r500, lead to three important results. First, the data support the conclusion that excess heating of the intracluster medium (or a combination of heating and condensation of the coldest gas) has altered its thermodynamic state from that expected in a simple, gravitationally dominated system; however, this excess heat is primarily limited to the central regions of clusters (r < 0.15r500). Secondly, the intrinsic scatter in the centre-excised luminosity–mass relation is remarkably small, being bounded at the <10 per cent level in current data; for the hot, massive clusters under investigation, this scatter is smaller than in either the temperature–mass or YX–mass relations (10–15 per cent). Thirdly, the evolution with redshift of the scaling relations is consistent with the predictions of simple, self-similar models of gravitational collapse, indicating that the mechanism responsible for heating the central regions of clusters was in operation before redshift 0.5 (the limit of our data) and that its effects on global cluster properties have not evolved strongly since then. Our results provide a new benchmark for comparison with numerical simulations of cluster formation and evolution.
Abstract
We present significantly improved measurements of turbulent velocities in the hot gaseous haloes of nearby giant elliptical galaxies. Using deep XMM–NewtonReflection Grating Spectrometer ...(RGS) observations and a combination of resonance scattering and direct line broadening methods, we obtain well bounded constraints for 13 galaxies. Assuming that the turbulence is isotropic, we obtain a best-fitting mean 1D turbulent velocity of ∼110 km s−1. This implies a typical 3D Mach number ∼0.45 and a typical non-thermal pressure contribution of ∼6 per cent in the cores of nearby massive galaxies. The intrinsic scatter around these values is modest – consistent with zero, albeit with large statistical uncertainty – hinting at a common and quasi-continuous mechanism sourcing the velocity structure in these objects. Using conservative estimates of the spatial scales associated with the observed turbulent motions, we find that turbulent heating can be sufficient to offset radiative cooling in the inner regions of these galaxies (<10 kpc, typically 2–3 kpc). The full potential of our analysis methods will be enabled by future X-ray micro-calorimeter observations.
This is the fourth of a series of papers in which we derive simultaneous constraints on cosmological parameters and X-ray scaling relations using observations of the growth of massive, X-ray ...flux-selected galaxy clusters. Our data set consists of 238 clusters drawn from the ROSAT All-Sky Survey and incorporates extensive follow-up observations using the Chandra X-ray Observatory. Here we examine the constraints on neutrino properties that are enabled by the precise and robust constraint on the amplitude of the matter power spectrum at low redshift available from our data. In combination with cluster gas mass fraction, cosmic microwave background, supernova and baryon acoustic oscillation data, and incorporating conservative allowances for systematic uncertainties, we limit the species-summed neutrino mass, Mν, to < 0.33 eV at 95.4 per cent confidence in a spatially flat, cosmological constant (ΛCDM) model. In a flat ΛCDM model where the effective number of neutrino species, Neff, is allowed to vary, we find Neff= 3.4+0.6−0.5 (68.3 per cent confidence, incorporating a direct constraint on the Hubble parameter from Cepheid and supernova data). We also obtain results with additional degrees of freedom in the cosmological model, in the form of global spatial curvature (Ωk) and a primordial spectrum of tensor perturbations (r and nt). The results are not immune to these generalizations; however, in the most general case we consider, in which Mν, Neff, curvature and tensors are all free, we still obtain Mν < 0.70 eV and Neff= 3.7 ± 0.7 (at, respectively, the same confidence levels as above). These results agree well with recent work using independent data and highlight the importance of measuring cosmic structure and expansion at low as well as high (z∼ 1100) redshifts. Although our cluster data extend to redshift z= 0.5, the direct effect of neutrino mass on the growth of structure at late times is not yet detected at a significant level.
We present a statistically complete sample of very X-ray luminous galaxy clusters detected in the MAssive Cluster Survey (MACS). This second MACS release comprises all 34 MACS clusters with nominal ...X-ray fluxes in excess of 2 × 10−12 erg s−1 cm−2 (0.1–2.4 keV) in the ROSAT Bright Source Catalogue; two-thirds of them are new discoveries. Extending over the redshift range from 0.3 to 0.5, this subset complements the complete sample of the 12 most distant MACS clusters (z > 0.5) published in 2007 and further exemplifies the efficacy of X-ray selection for the compilation of samples of intrinsically massive galaxy clusters. Extensive follow-up observations with Chandra/ACIS led to three additional MACS cluster candidates being eliminated as (predominantly) X-ray point sources. For another four clusters – which, however, remain in our sample of 34 – the point-source contamination was found to be about 50 per cent. The median X-ray luminosity of 1.3 × 1045 erg s−1 (0.1–2.4 keV, Chandra, within r500) of the clusters in this subsample demonstrates the power of the MACS strategy to find the most extreme and rarest clusters out to significant redshift. A comparison of the optical and X-ray data for all clusters in this release finds a wide range of morphologies with no obvious bias in favour of either relaxed or merging systems.
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