Baryon Crisis and Cluster Mass Estimates

I report the current status on the determinations of the baryon fractions and dynamical/lensing masses of galaxy clusters as well as the σ T relationship, making use of all the published data in literature which include 304 measurements for baryon fractions, 320/21 data points for masses of intracluster gas/cluster galaxies, (152+228)/72 data points for cluster masses derived from X-ray emitting gas/optical galaxies based on the hydrostatic equilibrium hypothesis, 46/33 measurements for the projected cluster masses obtained from strong/weak lensing. A straightforward statistical analysis yields the following features: (1)The cluster baryon fraction indeed shows an increasing tendency to reach a value of ∼ 30% at large cluster radius. (2)The dynamical cluster masses are in fairly good agreement with the masses determined by weak lensing technique; (3)The cluster masses provided by strong lensing and other methods are essentially consistent within a factor of ∼ 2. (4)The cluster σ − T relationship is in concordance with the scenario that overall galaxy clusters are the well relaxed dynamical systems. These results are strongly suggestive of a low-mass density universe (Ωm < 0.3), in which the fraction of baryonic matter (∼ 30%) is not very small !