Impacts of source properties on strong lensing by rich galaxy clusters

We use a high-resolution N-body simulation to investigate the influence of background galaxy properties, including redshift, size, shape, and clustering, on the efficiency of forming giant arcs by gravitational lensing of rich galaxy clusters. Two large sets of ray-tracing simulations are carried out for 10 massive clusters at two redshifts, i.e., z l ∼ 0.2 and 0.3. The virial mass (M vir) of the simulated lens clusters at z ∼ 0.2ranges from 6.8 × 1014 h -1 M · to 1.1 × 1015 h -1 M ·. The information of background galaxies brighter than 25 mag in the I-band is taken from the Cosmological Evolution Survey (COSMOS) imaging data. Around 1.7 × 105 strong lensing realizations with these images as background galaxies have been performed for each set. We find that the efficiency for forming giant arcs for z l = 0.2 clusters is broadly consistent with observations. Our study on control source samples shows that the number of giant arcs is decreased by a factor of 1.05 and 1.61 when the COSMOS redshift distribution of galaxies is adopted, compared to the cases where all the galaxies were assumed to be in a single source plane at z l = 1.0 and z l = 1.5, respectively. We find that the efficiency of producing giant arcs by rich clusters is weakly dependent on the source size and clustering. Our principal finding is that a small proportion (∼ 1/3) of galaxies with elongated shapes (e.g., ellipticity ε = 1 - b/a > 0.5) can boost the number of giant arcs substantially. Compared with recent studies where a uniform ellipticity distribution from 0 to 0.5 is used for the sources, the adoption of directly observed shape distribution increases the number of giant arcs by a factor of ∼ 2. Our results indicate that it is necessary to account for source information and survey parameters (such as point-spread function, seeing) to make correct predictions of giant arcs and further to constrain the cosmological parameters. © 2009. The American Astronomical Society. All rights reserved.