Physical and dynamical properties of two clusters of galaxies derived from X-ray data.

We analyze the Einstein IPC X-ray images of two clusters of galaxies: ABCG 85 and ABCG 2199. We have developed a new method, including a code which fully reproduces the IPC spatial and spectral properties and synthesizes cluster images for various kinds of temperature and density distributions. The differences between the synthetic and observed images are minimized pixel per pixel, leading to the best sets of parameters. We show that ABCG 85 is a double structured cluster with a main spherically symmetric gas component close to isothermal (temperature ~9 keV). ABCG 2199 has an elliptical shape, and its ICM temperature cannot be well derived. For each cluster, the various kinds of density profiles lead to similar results: very small core radii (much smaller than previously derived) and flat density slopes (B~0.44). We compute X-ray gas masses and find relatively small values: 3 10^13^, M_sun_ and 0.3 10^13^ M_sun_ within R_I_ = 1 Mpc and 0.3 Mpc (where R_I_, is the image radius) for ABCG 85 and ABCG 2199 respectively. Using the hydrostatic assumption, we find the binding mass to be about 8- 10 times the ICM mass within R_I_. By analyzing the ratio of the binding to ICM densities, we find that the unseen matter is highly peaked near the cluster center within a typical radius of 200 kpc. We argue that this is only possible if the velocity dispersion of the unseen matter is smaller than that of the ICM.