A COMPARISON OF X-RAY AND STRONG LENSING PROPERTIES OF SIMULATED X-RAY-CLUSTERS

We use gas-dynamical simulations of galaxy clusters to compare their X -ray and strong lensing properties. Special emphasis is laid on mass e stimates. The cluster masses range between 6 x 10(14) and 4 x 10(15) M (.), and they are examined at redshifts between 1 and 0. We compute th e X-ray emission of the intracluster gas by thermal bremsstrahlung, ad d background contamination, and mimic imaging and spectral observation s with current X-ray telescopes. Although the beta model routinely pro vides excellent fits to the X-ray emission profiles, the derived masse s are typically biased low because of the restricted range of radii wi thin which the fit can be done. For beta values of similar to 2/3, whi ch is the average in our numerically simulated sample, the mass is typ ically underestimated by similar to 40 per cent. The masses of cluster s that exhibit pronounced substructure are often substantially underes timated. We suggest that the ratio between peak temperature and emissi on-weighted average cluster temperature may provide a good indicator f or ongoing merging and, therefore, for unreliable mass estimates. X-ra y mass estimates are substantially improved if we fit a King density p rofile rather than the beta model to the X-ray emission, thereby dropp ing the degree of freedom associated with beta. Clusters selected for their strong lensing properties are typically dynamically more active than typical clusters. Bulk flows in the intracluster gas contain a la rger than average fraction of the internal energy of the gas in such o bjects, hence the measured gas temperatures are biased low. The bulk o f the optical depth for are formation is contributed by clusters with intermediate rather than high X-ray luminosity. Arcs occur predominant ly in clusters that exhibit substructure and are not in an equilibrium state. Finally, we explain why the X-ray emission of some observed ar e clusters is cooler than predicted from the are geometry. All cluster s for which this happens in our simulations show structure in velocity space, indicating ongoing merging along the line of sight. The temper ature discrepancy is probably a projection effect.