X-RAY-CLUSTERS FROM A HIGH-RESOLUTION HYDRODYNAMIC PPM SIMULATION OF THE COLD DARK-MATTER UNIVERSE

A new three-dimensional hydrodynamic code based on the piecewise parabolic method (PPM) is utilized to compute the distribution of hot ps in the standard COBE-normalized cold dark matter (CDM) universe. Utilizing periodic boundary conditions, a box with size 85 h-1 Mpc, having cell size 0.31 h-1 Mpc, is followed in a simulation with 270(3) = 10(7.3) cells. Adopting standard parameters determined from COBE and light-element nucleosynthesis, sigma8 = 1.05, OMEGA(b) = 0.06, we find the X-ray-emitting clusters, compute the luminosity function at several wavelengths, the temperature distribution, and estimated sizes, as well as the evolution of these quantities with redshift. The results, which are compared with those obtained in the preceding paper (Kang et al. 1994a), may be used in conjunction with ROSAT and other observational data sets. Overall, the results of the two computations are qualitatively very similar with regard to the trends of cluster properties, i.e., how the number density, radius, and temperature depend on luminosity and redshift. The total luminosity from clusters is approximately a factor of 2 higher using the PPM code (as compared to the 'total variation diminishing'' [TVD] code used in the previous paper) with the number of bright clusters higher by a similar factor. The primary conclusions of the prior paper, with regard to the power spectrum of the primeval density perturbations, are strengthened: the standard CDM model, normalized to the COBE microwave detection, predicts too many bright X-ray emitting clusters, by a factor probably in excess of 5. The comparison between observations and theoretical predictions for the evolution of cluster properties, luminosity functions, and size and temperature distributions should provide an important discriminator among competing scenarios for the development of structure in the universe.