EVOLUTION OF X-RAY-CLUSTERS OF GALAXIES AND SHOCK HEATING OF THE INTRACLUSTER MEDIUM

Evolutions of spherical X-ray clusters of galaxies are studied by usin g an N-body + total variation diminishing (TVD) mesh code. We consider a growth of density perturbation of 10(15) M-circle dot composed of d ark matter and gas in a cold dark matter-dominated universe with Omega (0) = 1 or 0.2. When the perturbation collapsed at z similar to 1, a s hock front appears at r similar to 0.1 Mpc, moving outward as ambient gas accretes toward cluster center. The shock front separates the inne r X-ray-emitting, hot region from the outer cool region. In the former , gas is almost in hydrostatic equilibrium but with small radial infal l (similar to 100 km s(-1)) being left, while in the latter, gas falls almost freely and emits no X-rays. Gas inside the shock is strongly c ompressed and heated by shock so that X-ray luminosity rapidly rises i n the early stage (until temperature reaches about virial). In the lat e stage, on the other hand, the X-ray luminosity rises only gradually due partly to the expansion of the inner high-temperature region and p artly to the increase of X-ray emissivity of gas as the result of cont inuous adiabatic compression inside the shock. We also find that the d ensity distribution is generally less concentrated in a lower density universe and, hence, X-ray luminosity rises more slowly than in a high er density universe. The shock front structure, which was not clearly reserved in the previous SPH simulations, is clearly captured by the p resent simulations. Our results confirm that shock heating plays an im portant role in the heating process of the intracluster medium. In add ition, we find that a sound wave propagates outward, thereby producing modulations with amplitudes of similar to 10% in the radial temperatu re and density profiles which, in turn, cause time variations in the s trength of the shock. Such modulations, if observed, could be used as a probe to investigate the internal structure of clusters and the init ial temperature of gas.