The Evolution of X‐Ray Clusters in a Low‐Density Universe

Abstract

We present results of N-body/gasdynamical simulations designed to investigate the evolution of X-ray clusters in a flat, low-density, Λ-dominated cold dark matter (CDM) cosmogony. The simulations include self-gravity, pressure gradients and hydrodynamical shocks, but neglect radiative cooling. The density profile of the dark matter component can be fitted accurately by the simple formula originally proposed by Navarro, Frenk & White to describe the structure of clusters in a CDM universe with Ω = 1. In projection, the shape of the dark matter radial density profile and the corresponding line-of-sight velocity dispersion profile are in very good agreement with the observed profiles for galaxies in the CNOC sample of clusters. This suggests that galaxies are not strongly segregated relative to the dark matter in X-ray luminous clusters. The gas in our simulated clusters is less centrally concentrated than the dark matter, and its radial density profile is well described by the familiar β-model. As a result, the average baryon fraction within the virial radius (r vir ) is only 85-90% of the universal value and is lower nearer the center. The total mass and velocity dispersion of our clusters can be accurately inferred (with ∼ 15% uncertainty) from their X-ray emission-weighted temperature. We generalize Kaiser's scalefree scaling relations to arbitrary power spectra and low-density universes and show that simulated clusters generally follow these relations. The agreement between the simulations and the analytical results provides a convincing demonstration of the soundness of our gasdynamical numerical techniques. Although our simulated clusters resemble observed clusters in several respects, the slope of the luminosity-temperature relation implied by the scaling relations, and obeyed by the simulations, is in disagreement with observations. This suggests that non-gravitational effects such as preheating or cooling must have played an important role in determining the properties of the observed X-ray emission from galaxy clusters.

Thermodynamical Properties of the ICM from Hydrodynamical Simulations

“…Indeed, Allen et al (2004) resorted to the set of SPH clusters simulated by Eke et al (1998) to calibrate the correction factor that one needs to apply to extrapolate the baryon fraction computed at r 2500 , which is the typical radius at which it is measured, to the cosmic value. However, since this set of simulations does not Squares indicate runs where cooling is switched off at z < 2, while triangles are for non-radiative simulations (from Kravtsov et al 2005).…”

Measuring Omega0 using cluster evolution

“…These usually include shock heating but no radiative cooling or heating from any source. Such experiments (NFW; Evrard, Metzler & Navarro 1996;Eke, Navarro & Frenk 1998;Bryan & Norman 1998;Frenk et al 1998) suggest that βTM = 1.0 is a reasonable choice, and it is adopted as the default value in this paper, although the dependence of the results on this assumption will be investigated in Section 4. Values returned from different types of hydrodynamical simulations for a variety of cosmologies range between 1 and 1.3 (see Bryan & Norman 1998), with a slight preference for larger values of βTM when Ω0 is larger.…”

Cosmology and astrophysics from relaxed galaxy clusters – V. Consistency with cold dark matter structure formation

“…Jenkins et al 2001;Evrard et al 2002;Tinker et al 2008), the ratio of baryonic mass to CDM in galaxy clusters (e.g. Eke et al 1998;Kay et al 2004;Borgani & Kravtsov 2011), and the distribution of mass within the structures that form hierarchically in the Universe (e.g. Bullock et al 2001;Navarro et al 2004Navarro et al , 1997Gao et al 2008).…”