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Comparison of the high resolution X-ray ROSAT HRI image of A2218 with the optical HST image shows several interesting correlations. The X-ray emission within a 1 radius core is resolved into several components; the central dominant galaxy does not coincide with either of them or the emission centroid. The major X-ray peak is an elongated feature which coincides with optical arcs at r=20 from the cD. We speculate that this may be lensed X-ray emission, for example, of the same object lensed in the optical. Alternatively, this feature may be a merger shock, or a gas trail of an infalling subgroup. Two other X-ray enhancements are close to the two major mass concentrations known from the lensing analysis. Both lensing and a merger are likely. Previous X-ray derivations of the A2218 mass used the data with angular resolution that blurred the features mentioned above into a broad constant core. As the HRI data show, such a core does not exist. Because of this, the hydrostatic estimate of the projected mass within the lensing radius can in principle be increased by a factor of 1.4 (and the mass within a sphere by a factor of 2.6) compared to previous analyses. However, for a merging cluster, the hydrostatic analysis is generally inapplicable. Most other lensing clusters are more distant than A2218 and obtaining adequate X-ray data for them is even more difficult. Together with the likely overestimation of mass by the lensing analysis (as in the simulations), oversimplification of the gas model resulting from inadequate resolution may account for the lensing/X-ray mass discrepancy as suggested for A2218. (ABRIDGED)
We present results from two observations (combined exposure of ~17 ks) of galaxy cluster A2218 using the Advanced CCD Imaging Spectrometer on board the Chandra X-ray Observatory that were taken on October 19, 1999. Using a Raymond-Smith single temper
We present results from a deep photometric study of the rich galaxy cluster Abell 2218 (z=0.18) based on archival HST WFPC2 F606W images. These have been used to derive the luminosity function to extremely faint limits (M_{F606W}=-13.2 mag, mu_{0}=24
Determination of cluster masses is a fundamental tool for cosmology. Comparing mass estimates obtained by different probes allows to understand possible systematic uncertainties. The cluster Abell 315 is an interesting test case, since it has been cl
We report Chandra X-ray observations and optical weak-lensing measurements from Subaru/Suprime-Cam images of the double galaxy cluster Abell 2465 (z=0.245). The X-ray brightness data are fit to a beta-model to obtain the radial gas density profiles o
We determine colour gradients of $-0.15 pm 0.08$ magnitudes per decade in radius in F450W$-$F606W and $-0.07 pm 0.06$ magnitudes per decade in radius in F606W$-$F814W for a sample of 22 E/S0 galaxies in Abell 2218. These gradients are consistent with