Hot gas in the cold dark matter scenario: X-ray clusters from a high-resolution numerical simulation

We exmaine the distribution of hot gas in a standard CDM model of theuniverse using high resolution hydrodynamic simulations. Adopting standardparameters determined from COBE and light element nucleosynthesis,$\sigma_8=1.05$, $\Omega_b=0.06$ and assuming $h=0.5$, we find the X-rayemitting clusters, compute the luminosity function at several wavelengths, thetemperature distribution and estimated sizes as well as the evolution of thesequantities with redshift. This standard CDM model, normalized to COBE, producesapproximately 5 times too much emission from clusters having$L_x>10^{43}$erg/s, a not unexpected result. If all other parameters wereunchanged, we would expect adequate agreement for $\sigma_8=0.6$. This providesa new and independent argument for lower small scale power than standard CDM atthe $8h^{-1}$Mpc scale. The background radiation field at 1keV due to clustersin this model is approximately $1/3$ of the observed background which, aftercorrection for numerical effects, again indicates approximately 5 times toomuch emission and the appropriateness of $\sigma_8=0.6$. If we had used theobserved ratio of gas to total mass in clusters, rather than basing the meandensity on light element nucleosynthesis, then the computed luminosity of eachcluster would have increased still further, by a factor of approximately ten.Examining the ratio of gas to total mass in the clusters (which we find to beanti-biased by a factor of approximately 0.6), normalized to $\Omega_bh^2=0.015$, and comparing to observations, we conclude, in agreement with S.White, that the cluster observations argue for an open universe.Comment: 35p plaintex to appear in The Astrophysical Journal on June 10, 199