The structure of the ICM from High Resolution SPH simulations

Using a set of hydrodynamical simulations of 9 galaxy clusters with masses in the range 1.5 10^{14} M_sun < M_vir < 3.4 10^{15} M_sun, we have studied the density, temperature and X-ray surface brightness profiles of the intracluster medium in the regions around the virial radius. We have analyzed the profiles in the radial range well above the cluster core, the physics of which are still unclear and matter of tension between simulated and observed properties, and up to the v...

We demonstrate that all properties of the hot X-ray emitting gas in galaxy clusters are completely determined by the underlying dark matter (DM) structure. Apart from the standard conditions of spherical symmetry and hydrostatic equilibrium for the gas, our proof is based on the Jeans equation for the DM and two simple relations which have recently emerged from numerical simulations: the equality of the gas and DM temperatures, and the almost linear relation between the DM ve...

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...

An analytical model for the postcollapse equilibrium structure of virialized objects which condense out of the cosmological background universe is described and compared with observations and simulations of cosmological halos. The model is based upon the assumption that virialized halos are isothermal, which leads to a prediction of a unique nonsingular isothermal sphere for the equilibrium structure, with a core density which is proportional to the mean background density at...

(ABRIDGED) We analyze the X-ray properties of a sample of local and high redshift galaxy clusters extracted from a large cosmological hydrodynamical simulation. This simulation has been realized using the Tree+SPH code GADGET-2 for a LambdaCDM model. In our analysis, we consider only objects with T_ew >2 keV and adopt an approach that mimics observations, associating with each measurement an error comparable with recent observations and providing best-fit results via robust t...

We compare the results of Eulerian hydrodynamic simulations of cluster formation against virial scaling relations between four bulk quantities: the cluster mass, the dark matter velocity dispersion, the gas temperature and the cluster luminosity. The comparison is made for a large number of clusters at a range of redshifts in three different cosmological models (CHDM, CDM and OCDM). We find that the analytic formulae provide a good description of the relations between three o...

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...

We investigate evolution of the intracluster medium (ICM), considering the relaxation process between the ions and electrons. According to the standard scenario of structure formation, ICM is heated by the shock in the accretion flow to the gravitational potential well of the dark halo. The shock primarily heats the ions because the kinetic energy of an ion entering the shock is larger than that of an electron by the ratio of masses. Then the electrons and ions exchange the e...

Galaxy clusters exhibit remarkable self-similar behavior which allows us to establish simple scaling relationships between observable quantities and cluster masses, making galaxy clusters useful cosmological probes. Recent X-ray observations suggest that self-similarity may be broken in the outskirts of galaxy clusters. In this work, we analyze a mass-limited sample of massive galaxy clusters from the Omega500 cosmological hydrodynamic simulation to investigate the self-simil...

We will discuss here how structures observed in clusters of galaxies can provide us insight on the formation and evolution of these objects. We will focus primarily on X-ray observations and results from hydrodynamical $N$-body simulations. This paper is based on a talk given at the School of Cosmology Jose Plinio Baptista -- `Cosmological perturbations and Structure Formation' in Ubu/ES, Brazil.