Gravitational Shear, Flexion and Strong Lensing in Abell 1689

Abstract

We present a gravitational lensing analysis of the galaxy cluster Abell 1689, incorporating measurements of the weak shear, flexion, and strong lensing induced in background galaxies. This is the first time that a shapelet technique has been used to reconstruct the distribution of mass in this cluster, and the first time that a flexion signal has been measured using cluster members as lenses. From weak shear measurements alone, we generate a non-parametric mass reconstruction, which shows significant substructure corresponding to groups of galaxies within the cluster. Additionally, our galaxy-galaxy flexion signal demonstrates that the cluster galaxies can be well-fit by a singular isothermal sphere model with a characteristic velocity dispersion of $σ_v = 295\pm 40 km/s $. We identify a major, distinct dark matter clump, offset by 40$h^{-1}$kpc from the central cluster members, which was not apparent from shear measurements alone. This secondary clump is present in a parametric mass reconstruction using flexion data alone, and its existence is suggested in a non-parametric reconstruction of the cluster using a combination of strong and weak lensing. As found in previous studies, the mass profile obtained by combining weak and strong lensing data shows a much steeper profile than that obtained from only weak lensing data.