X - ray properties of the distant cluster Cl 0016 + 16

We present X-ray data on the distant cluster Cl0016+16 (z=0.5545) from ROSAT PSPC and HRI observations and use them to study the physics of the intracluster medium (ICM) and the dynamical state of the cluster. The surface brightness distribution is not only described by a spherically symmetric model but also by a twodimensional β-model fit. Subtracting an elliptical model cluster as defined by the best fit parameters of the two-dimensional model we find significant residuals, indicating an additional, extended X-ray source within the cluster. This source, likely to be a merging subcomponent of the cluster, coincides with a peak in the weak lensing mass map of Smail et. al. (1995). In the course of this analysis we present a new approach to quantify the significance of substructure in cluster X-ray images dominated by Poisson noise and smoothed with a Gauss filter. We determine the radial mass profile integrated out to a radius of 3Mpc and find for the total mass of the cluster a value of ∼ 1.4− 3.3× 10 M⊙ and ∼ 4.5× 10 14 M⊙ for the gas mass, yielding a gas–to–total mass ratio of 14 – 32%. There is no significant radial dependence of the gas–to–total mass ratio in the cluster.