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Extensive measurements of the X-ray background (XRB) yield a reasonably reliable characterization of its basic properties. Having resolved most of the cosmic XRB into discrete sources, the levels and spectral shapes of its main components can be used to probe both the source populations and also alternative cosmological and large-scale structure models. Recent observations of clusters seem to provide evidence that clusters formed earlier and are more abundant than predicted in the standard Λ cold dark matter (ΛCDM) model. This motivates interest in alternative models that predict enhanced power on cluster scales. We calculate predicted levels and spectra of the superposed emission from groups and clusters of galaxies in ΛCDM and in two viable alternative non-Gaussian and early dark energy models. The predicted levels of the contribution of clusters to the XRB in the non-Gaussian models exceed the measured level at low energies and levels of the residual XRB in the 2–8 keV band; these particular models are essentially ruled out. Our work demonstrates the diagnostic value of the integrated X-ray emission from clusters, by considering also its dependences on different metallicities, gas and temperature profiles, Galactic absorption, merger scenarios and on a non-thermal pressure component. We also show that the XRB can be used for an upper limit for the concentration parameter value. [ABSTRACT FROM AUTHOR]

We present a joint shear-and-magnification weak-lensing analysis of a sample of 16 X-ray-regular and 4 high-magnification galaxy clusters at 0.19 ≲ z ≲ 0.69 selected from the Cluster Lensing And Supernova survey with Hubble (CLASH). Our analysis uses wide-field multi-color imaging, taken primarily with Suprime-Cam on the Subaru Telescope. From a stacked-shear-only analysis of the X-ray-selected subsample, we detect the ensemble-averaged lensing signal with a total signal-to-noise ratio of ≃ 25 in the radial range of 200-3500 kpc h–1, providing integrated constraints on the halo profile shape and concentration-mass relation. The stacked tangential-shear signal is well described by a family of standard density profiles predicted for dark-matter-dominated halos in gravitational equilibrium, namely, the Navarro-Frenk-White (NFW), truncated variants of NFW, and Einasto models. For the NFW model, we measure a mean concentration of at an effective halo mass of . We show that this is in excellent agreement with Λ cold dark matter (ΛCDM) predictions when the CLASH X-ray selection function and projection effects are taken into account. The best-fit Einasto shape parameter is , which is consistent with the NFW-equivalent Einasto parameter of ∼0.18. We reconstruct projected mass density profiles of all CLASH clusters from a joint likelihood analysis of shear-and-magnification data and measure cluster masses at several characteristic radii assuming an NFW density profile. We also derive an ensemble-averaged total projected mass profile of the X-ray-selected subsample by stacking their individual mass profiles. The stacked total mass profile, constrained by the shear+magnification data, is shown to be consistent with our shear-based halo-model predictions, including the effects of surrounding large-scale structure as a two-halo term, establishing further consistency in the context of the ΛCDM model. [ABSTRACT FROM AUTHOR]