Strong Lensing In N-body Simulated Clusters

This thesis will mainly focus on the lensing properties of N-body simulated galaxy clusters. Firstly, we propose a new smoothing method for obtaining surface densities from discrete particle positions from numerical simulations. This is an essential step for many applications in gravitational lensing. This method is based on the "scatter" interpretation of the discrete density field in the Smoothed Particle Hydrodynamics. We use Monte Carlo simulations of uniform density fields and one isothermal ellipsoid to empirically derive the noise properties, and best smoothing parameters (such as the number of nearest neighbors used). A cluster from high-resolution simulations is then used to assess the reality of high-order singularities such as swallowtails and butterflies in caustics, which are important for the interpretation of substructures in gravitational lenses. We also compare our method with the Delaunay tesselation field estimator using the galaxy studied by Bradac et al. (2004), and find good agreements. We show that higher order singularities are not only connected with bound subhaloes but also with the satellite streams. However, the presence of high-order singularities are sensitive to not only the fluctuation amplitude of the surface density, but also the detailed form of the underlying smooth lensing potential (such as ellipticity and external shear).We use high-resolution N-body simulations to study the galaxy-cluster cross-sections and the abundance of giant arcs in the ACDM model. Clusters are selected from the simulations using the friends-of-friends method, and their cross-sections for forming giant arcs are analyzed. The background sources are assumed to follow a uniform ellipticity distribution from 0 to 0.5 and to have an area identical to a circular source with diameter 1". We find that the optical depth scales as the source redshift approximately as τ_1" = 2.25 × 10^-6/[1 + (z_s /3.14)^-3.42] (0.6 < z_s < 7). The amplitude is about 50% higher for an effective source diameter of 0.5". The optimal lens redshift for giant arcs with the length-to-width ratio (L/W) larger than 10 increases from 0.3 for z_s = 1, to 0.5 for z_s = 2,...