X-ray observations of Abell 2218 and implications for the sunyaev-zel'dovich effect

The Einstein Observatory has been used to obtain a high-resolution X-ray image and an X-ray flux measurement of the galaxy cluster Abell 2218. Aside from a minor contribution from the cD galaxy near the cluster center, the image is circularly symmetric and displays a smooth radial profile. The combined system of intracluster medium and galaxies was modeled as a gas in hydrostatic equilibrium in a common gravitational potential with an isothermal galaxy component. This model was then fitted in the least-squares sense to the X-ray surface brightness distribution and to the optically determined galaxy surface density profile to determine model parameters. In this context, the gas was found to be nominally isothermal, moderately dense, and very hot (10 keV<kT< 30 keV)--conditions consistent with the diminution in the cosmic microwave background radiation intensity reported in the direction of this cluster by some observers. In principle, the combination of such microwave measurements with X-ray and optical data allows the establishment of distances to truly remote clusters independently of the canonical chain of distance indicators and free from certain evolutionary effects. In pratice, however, the considerable imprecision inherent in this method of distance estimation, irrespective of uncertainties regarding the microwave measurements, prevents us from making a definitive statement about the distance to Abell 2218. We conclude by emphasizing the diagnostic capabilities of this analysis scheme for investigating the properties of the intracluster medium and related studies of cluster evolution