The radial structure of galaxy groups and clusters

We present results from a set of high (512^3 effective resolution), and ultra-high (1024^3) SPH adiabatic cosmological simulations of cluster formation aimed at studying the internal structure of the intracluster medium (ICM). We derive a self-consistent analytical model of the structure of the intracluster medium (ICM). We discuss the radial structure and scaling relations expected from purely gravitational collapse, and show that the choice of a particular halo model can ha...

We develop a model to describe the evolution of the intra-cluster X-ray emitting baryons, as they are included in the dark matter potential wells of galaxy clusters evolving through subsequent merging events in the framework of hierarchical clustering. The gas is assumed to re-adjusts to a new hydrostatic equilibrium after each merging event. Before merging it is gravitationally heated at the local virial temperature when bound in subclusters; at early $z$ the gas is preheate...

[abridged] The equilibria of the intracluster plasma (ICP) and of the gravitationally dominant dark matter (DM) are governed by the hydrostatic and the Jeans equation. Jeans, with the DM `entropy' set to K ~ r^\alpha and \alpha ~ 1.25 - 1.3 applying from groups to rich clusters, yields our radial \alpha-profiles. In the ICP the entropy run k(r) is mainly shaped by shocks, as steadily set by supersonic accretion of gas at the cluster boundary, and intermittently driven from th...

The dominant baryonic component of galaxy clusters is hot gas whose distribution is commonly probed through X-ray emission arising from thermal bremsstrahlung. The density profile thus obtained has been traditionally modeled with a beta-profile, a simple function with only three parameters. However, this model is known to be insufficient for characterizing the range of cluster gas distributions, and attempts to rectify this shortcoming typically introduce additional parameter...

The X-ray cluster gas density distribution in hydrostatic equilibrium is computed from the universal density profile of the dark matter halo recently proposed by Navarro, Frenk and White (1996, 1997). If one assumes the isothermality, the resulting distribution is well approximated by the conventional $\beta$-model. We predict the core radius $r_{c}$, the $\beta$-parameter, and the X-ray luminosity of clusters as a function of the temperature $T_{X}$ of clusters in some repre...

We present an analytic approach to predict gas density and temperature profiles in dark matter haloes. We assume that the gas density profile traces the dark matter density profile in outer parts of the haloes, as suggested by many hydrodynamic simulations. Under this assumption, the hydrostatic equilibrium uniquely fixes the two free parameters in the model, the mass-temperature normalization and the polytropic index, that determine the temperature profile. This enables us t...

We investigate the predicted present-day temperature profiles of the hot, X-ray emitting gas in galaxy clusters for two cosmological models - a current best-guess LCDM model and standard cold dark matter (SCDM). Our numerically-simulated "catalogs" of clusters are derived from high-resolution (15/h kpc) simulations which make use of a sophisticated, Eulerian-based, Adaptive Mesh-Refinement (AMR) code that faithfully captures the shocks which are essential for correctly modell...

In this note, I suggest that the beta-model used to fit the X-ray surface brightness profiles of extended sources, like groups and clusters of galaxies, has to be corrected when the counts are collected in a wide energy band comparable to the mean temperature of the source and a significant gradient in the gas temperature is observed. I present a revised version of the beta-model for the X-ray brightness that applies to a intracluster gas with temperature and density related ...

We review recent progress in the description of the formation and evolution of galaxy clusters in a cosmological context by using numerical simulations. We focus our presentation on the comparison between simulated and observed X-ray properties, while we will also discuss numerical predictions on properties of the galaxy population in clusters. Many of the salient observed properties of clusters, such as X-ray scaling relations, radial profiles of entropy and density of the i...

We present a simple model to describe the dark matter density, the gas density, and the gas temperature profiles of galaxy clusters. Analytical expressions for these quantities are given in terms of only five free parameters with a clear physical meaning: the mass M of the dark matter halo (or the characteristic temperature T_0), the characteristic scale radius a, the cooling radius in units of a (0<alpha<1), the central temperature in units of T_0 (0<t<1), and the asymptotic...