AN ARC SYSTEM WITH A RADIAL GRAVITATIONAL IMAGE IN THE CLUSTER MS-2137-23

This Letter presents the first detection of a radial gravitational image candidate in a cluster of galaxies. In addition, the field of the cluster MS 2137-23 (z = 0.315) contains a large arc and a few arclets. The radial image is embedded within the halo of the central cD galaxy and can be seen only with high-resolution images. The color and brightness of this image are similar to other arc(let)s and strongly favor the radial gravitational image hypothesis. The radial image implies a small core radius for the cluster. A geometrical configuration, with both a large arc and a radial image, provides a unique opportunity to model the center of a clusters potential and the dark matter distribution. We also suggest that the very faint diffuse stellar component inside the cluster core may trace the geometrical distribution of the dominant invisible mass. The observational data available for modeling are presented and discussed.