Gravitational Lensing by Nearby Clusters of Galaxies

We present an estimation of the expected number of arcs and arclets in a survey of nearby (z < 0.1) clusters of galaxies, which takes into account the observational constraints. We show that strong lensing effects are not common, but also that they are not as rare as usually stated. Indeed, for a given cluster, the predicted number of arcs strongly depends on the magnitude limit of the survey and the actual value of the seeing. We also describe the procedures and results of a search for gravitational arcs and arclets in a sample of 33 galaxy clusters, representative of the local cluster distribution and spanning the redshift range of 0.014 < z < 0.076. Only one new arc candidate was discovered, located ∼3 arcmin away from the center of the cluster Abell 3266 (z = 0.059), whose redshift was found to be z = 0.073. The assumption that a mass concentration around a bright cluster elliptical 16.″6 away from the arc candidate could explain this arc as a gravitational image requires the presence of a very massive substructure in this cluster (M/LV ∼ 163 M⊙/L⊙). Although such substructure cannot be completely discarded, the nature of the arc candidate most possibly corresponds to a disk galaxy belonging to A3266. Our simplified theoretical model predicts that the probability of finding at least one gravitational arc in the sample investigated is 25%, in good agreement with the actual number of arcs found, N = 1 or 0, either adopting the arc in A3266 as a gravitational image or not. We conclude that a deep survey of the central regions of low-z galaxy clusters, with very good image quality, should allow significant progress in the mapping of their central mass concentration.