Arc Statistics in Clusters: Galaxy Contribution

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Abstract
The frequency with which background galaxies appear as long arcs as a result of gravitational lensing by foreground clusters of galaxies has recently been found by Bartelmann et al. to be a very sensitive probe of cosmological models. They have found that such arcs would be expected far less frequently than observed (by an order of magnitude) in the currently favored model of the universe, with a large cosmological constant, ΩΛ ~ 0.7. Here we analyze whether including the effect of cluster galaxies on the likelihood of clusters to generate long-arc images of background galaxies can change the statistics. Taking into account a variety of constraints on the properties of cluster galaxies, we find that there are not enough sufficiently massive galaxies in a cluster for them to significantly enhance the cross section of clusters and generate long arcs. We find that cluster galaxies typically enhance the cross section by only 15%.
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