Evolution of X‐Ray Clusters of Galaxies and Shock Heating of the Intracluster Medium

Evolutions of X-ray clusters of galaxies are studied by N-body (shell model)+ mesh code (TVD) simulations on the assumption of spherical symmetry. Weconsider a density perturbation of $10^{15} M_{\odot}$ composed of dark matterand gas in cold dark matter dominated universe with the cosmological densityparameter, $\Omega_0 = 1$ or $0.2$. A shock front appears during its initialcollapse, moving outward as ambient gas accretes towards cluster center. Theshock front separates the inner X-ray emitting, hot region, where gas is almostin hydrostatic equilibrium but with small radial infall ($\sim 100$km s$^{-1}$)being left, from the outer cool region. Gas inside the shock is stronglycompressed and heated by shock so that X-ray luminosity rapidly rises in theearly stage. In the late stage, however, the X-ray luminosity rises onlygradually due partly to the expansion of the inner high temperature region andpartly to the increase of X-ray emissivity of gas as the results of continuousadiabatic compression inside the shock. The shock front structure, which wasnot clearly resolved in the previous SPH simulations, is clearly captured bythe present simulations. In addition, we find a sound wave propagating outward,thereby producing spatial modulations with amplitudes of $\sim$ 10 % in theradial temperature and density profiles and time variations in the strength ofthe shock. Such modulations, if observed, could be used as a probe toinvestigate the structure of clusters.Comment: 33 pages and 12 figures. Submitted to Ap