GRAVITATIONAL LENS MODELS OF ARCS IN CLUSTERS

It is now well established that the luminous arcs discovered in clusters of galaxies, in particular those in Abell 370 and Cluster 2244-02, are produced by gravitational lensing of background sources. Since the arcs are well-resolved images of an extended source, they provide an unique opportunity for the study of the mass distribution in clusters and of the nature of distant young galaxies. We have modeled the arcs and put constraints on the distribution of the mass in the clusters and the shape and size of the sources. Our models require, as expected, a large amount of dark matter in the clusters and a mass-to-blue-light ratio for the cluster which exceeds 100 M⊙/L⊙ and could be as high as 103 M⊙/L⊙ depending on cosmological parameters and the distribution of the dark matter. Furthermore, we find that in the case of the arc in A370 the dark matter must have a different distribution than the luminous galaxies, while for the arc in Cl 2244 the dark matter can have a distribution similar to that of the light matter (galaxies) or a separate distribution. The details of the dark matter distributions are investigated further for the A370 lens, and we find that a distribution resembling that of a singular, truncated isothermal gas sphere with a reasonable velocity dispersion for the dark matter and a reasonable mass-to-light ratio for the galaxies fits the observations. Other, nonsingular distributions produce acceptable fits to the data if they are centrally condensed (characteristic size < 100 kpc). We also discuss possible explanations for the surface brightness fluctuations of the Cl 2244 arc and the deviation from circularity of the A370 arc.