The radial structure of galaxy groups and clusters

We present some of the results of an ongoing collaboration to sudy the dynamical properties of galaxy clusters by means of high resolution adiabatic SPH cosmological simulations. Results from our numerical clusters have been tested against analytical models often used in X-ray observations: $\beta$ model (isothermal and polytropic) and those based on universal dark matter profiles. We find a universal temperature profile, in agreement with AMR gasdynamical simulations of gala...

In this paper we have made an attempt to derive the radial profiles of density and temperature of intracluster gas based on the two well-established facts at present: the X-ray observed surface brightness of clusters described by the standard beta model and the (NFW) universal density profile as the underlying dark matter distribution. We have numerically solved the hydrostatic equation by demanding that the volumed-averaged baryon fraction of a cluster should asymptotically ...

We describe a theoretical framework to compute the cluster gas distribution in hydrostatic equilibrium embedded in a class of spherical dark matter halo potentials. Unlike the conventional isothermal $\beta$-model, the present method provides a physical basis to directly probe the shape of dark matter halo from the observed X-ray surface brightness and temperature profiles of clusters of galaxies. Specifically, we examine the extent to which the resulting gas density and X-ra...

Clusters of galaxies are studied from a theoretical point of view, comparing with observational results whenever possible. The problem is approached both analytically as well as by means of high-resoultion numerical simulations. The dark matter halo, the hot intracluster gas, and the stellar component are investigated separately. Numerical clusters are consistent with a relatively simple scenario, in which these objects form around local maxima of the primordial density field...

In this Letter we present the radial temperature profiles of three X-ray clusters (A119, A2255 and A2256) reconstructed from a combination of the X-ray surface brightness measurements and the universal density profile as the underlying dark matter distribution. Our algorithm is based on the hydrostatic equilibrium for intracluster gas and the universality of the total baryon fraction within the virial radius. The scaled temperature profiles of these three clusters appear to b...

We constrain gas and dark matter (DM) parameters of galaxy groups and clusters, by comparing X-ray scaling relations to theoretical expectations, obtained assuming that the gas is in hydrostatic equilibrium with the DM and follows a polytropic relation. We vary four parameters: the gas polytropic index Gamma, its temperature at large radii T_xi, the DM logarithmic slope at large radii zeta and its concentration c_vir. When comparing the model to the observed mass-temperature ...

We present simulations of the formation and evolution of galaxy clusters in the Cold Dark Matter cosmogony. Clusters with a wide range of mass were selected from previous N-body models, and were resimulated at higher resolution using a combined N-body/Smooth Particle Hydrodynamics code. The effects of radiative cooling on the gas are neglected. While many present-day clusters are predicted to be undergoing mergers, the density profiles of those that are approximately in equil...

Using high-resolution non-radiative hydrodynamic simulations of galaxy clusters we obtain simple analytic formulae for DM and gas distribution in the spherical approximation. We derive fits for the DM density, velocity dispersion and velocity anisotropy. We use these models to test the dynamical equilibrium hypothesis through the Jeans equation: we find that this is satisfied to good accuracy. This result show that our fits constitute a self-consistent dynamical model. We the...

As the end products of the hierarchical process of cosmic structure formation, galaxy clusters present some predictable properties, like those mostly driven by gravity, and some others, more affected by astrophysical dissipative processes, that can be recovered from observations and that show remarkable "universal" behaviour once rescaled by halo mass and redshift. However, a consistent picture that links these universal radial profiles and the integrated values of the thermo...

We analyse the radial structure of self-gravitating spheres consisting of multiple interpenetrating fluids, such as the X-ray emitting gas and the dark halo of a galaxy cluster. In these dipolytropic models, adiabatic dark matter sits in equilibrium, while the gas develops a gradual, smooth, quasi-stationary cooling flow. Both affect and respond to the collective gravitational field. We find that all subsonic, radially continuous, steady solutions require a non-zero minimum c...