A detailed analysis of the dynamical state of the cluster of galaxies A2218 in X-rays

We reanalyze ROSAT PSPC and HRI data of the cluster of galaxies A2218 in or der to investigate its dynamical state. To reveal the cluster's substructur e in X-rays, we construct symmetric cluster models by fitting a two-dimensi onal isothermal beta-model, which we subsequently subtract from the origina l data. Study of the remaining structures and their significance gives new insight into existing substructure, and therefore indications concerning th e dynamical state of the cluster, which has not yet been clearly visualized in X-rays. The present analysis enables us not only to qualitatively deter mine the dynamical state of the clusters, but also to draw conclusions abou t the significance of existing substructure in giving real numbers. A2218 r eveals significant structure after the subtraction, providing clear evidenc e that it is going through a merger phase. The X-ray morphology is in agree ment with the surface mass density map obtained by analysis based on weak l ensing. The subgroup falling in the center of A2218 is most likely on its f irst infall.