We have performed a uniform analysis on the ROSAT HRI and ASCA GIS/SIS data of 80 clusters of galaxies in the redshift range, 0.1 < zobs < 1. The samples include all the clusters in the redshift range observed with both the ROSAT HRI and ASCA, except for the three clusters which were observed away from the center of the telescope field of views. We determined the average X-ray temperatures of the clusters with ASCA. On the other hand, the surface brightness distributions were studied with the ROSAT HRI utilizing the isothermal β-model and the NFW-SSM model.
We found no significant redshift (zobs) dependence in the X-ray parameters, the temperature, T, the β parameter (or the B parameter for the NFW), the core radius rc (or the scale parameter rs), and the central electron density ne0. However, if we define the virial radius by ρ(rvir)=Δc ρcrit (zobs), where ρ(r) is the average density inside a radius r, ρcrit(z) the critical density at z, and Δc ~ 200, we find the virial radius rvir shows zobs dependency. Since the dependency comes from the z dependency of ρcrit, we consider it is more preferable that the collapse redshift zcol is significantly different from zobs.
Among the X-ray parameters, the core radius shows the largest cluster-to-cluster dispersions of more than an order of magnitude, even if we restrict the samples to morphologically "regular" clusters. In the histogram of core radius distribution, we find double peaks at about 60 kpc and 220 kpc. On the other hand, the surface brightness profiles of nine regular clusters were better fitted with a double β-model than a single β-model. The average of the two core radii of the nine clusters were about 60 kpc and 260 kpc respectively. Moreover, about 80% of regular clusters were consistent with having similar double β structure. These results suggest that most of the clusters contain a structure which can be approximated with a double β-model and that, depending on the surface brightnesses of the two cores, clusters are recognized either as a single-β cluster with a large/small core radius or a double-β cluster. Since the radiative cooling time of intracluster gas in the smaller core is estimated to be much shorter than the age of the cluster, we make the conjecture that the intracluster gas gradually concentrates towards the center to evolve from an outer-core-dominant cluster to an inner-core-dominant cluster.
Finally we have estimated the density parameter of the universe to be Ω0 = 0.28 ± 0.10 h50-1/2, where we have considered the systematic errors from the telescope/detector calibrations and the uncertainty in the virial radius.