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 parab olic method (PPM) is utilized to compute the distribution of hot ps in the standard COBE-normalized cold dark matter (CDM) universe. Utilizi ng periodic boundary conditions, a box with size 85 h-1 Mpc, having ce ll 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-e lement nucleosynthesis, sigma8 = 1.05, OMEGA(b) = 0.06, we find the X- ray-emitting clusters, compute the luminosity function at several wave lengths, the temperature distribution, and estimated sizes, as well as the evolution of these quantities with redshift. The results, which a re compared with those obtained in the preceding paper (Kang et al. 19 94a), may be used in conjunction with ROSAT and other observational da ta sets. Overall, the results of the two computations are qualitativel y very similar with regard to the trends of cluster properties, i.e., how the number density, radius, and temperature depend on luminosity a nd redshift. The total luminosity from clusters is approximately a fac tor of 2 higher using the PPM code (as compared to the 'total variatio n diminishing'' [TVD] code used in the previous paper) with the number of bright clusters higher by a similar factor. The primary conclusion s of the prior paper, with regard to the power spectrum of the primeva l density perturbations, are strengthened: the standard CDM model, nor malized to the COBE microwave detection, predicts too many bright X-ra y emitting clusters, by a factor probably in excess of 5. The comparis on between observations and theoretical predictions for the evolution of cluster properties, luminosity functions, and size and temperature distributions should provide an important discriminator among competin g scenarios for the development of structure in the universe.