THE EVOLUTION OF X-RAY-CLUSTERS IN A COLD PLUS HOT DARK-MATTER UNIVERSE

We present the first self-consistently computed results on the evoluti on of X-ray properties of galaxy clusters in a cold + hot dark matter (CHDM) model. We have performed a hydrodynamic plus N-body simulation for the COBE-compatible CHDM model with standard mass components: Omeg a(hot) = 0.3, Omega(cold) = 0.6 and Omega(baryon) = 0.1 (h = 0.5). In contrast with the CDM model, which fails to reproduce the observed tem perature distribution function dN/dT (Bryan et al. 1994b), the CHDM mo del fits the observational dN/dT quite well. Our results on X-ray lumi nosity are less firm but even more intriguing. We find that the result ing X-ray luminosity functions at redshifts z = 0.0, 0.2, 0.4, 0.7 are well fit by observations, where they overlap. The fact that both temp eratures and luminosities provide a reasonable fit to the available ob servational data indicates that, unless we are missing some essential physics, there is neither room nor need for a large fraction of gas in rich clusters: 10% (or less) in baryons is sufficient to explain thei r X-ray properties. We also see a tight correlation between X-ray lumi nosity and gas temperature.