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. $z_{\rm l} \sim 0.2$ and 0.3. The virial mass ($M_{\rm vir}$) of the simulated lens clusters at $z\sim0.2$ ranges from $6.8\times10^{14} h^{-1} {M_{\odot}}$ to $1.1\times 10^{15} h^{-1} M_{\odot}$. The information of background galaxies brighter than 25 magnitude in the $I$-band is taken from Cosmological Evolution Survey (COSMOS) imaging data. Around $1.7\times 10^5$ 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 $z_{\rm l}=0.2$ clusters is broadly consistent with observations. 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 ($\sim 1/3$) of galaxies with elongated shapes (e.g. ellipticity $\epsilon=1-b/a>0.5$) 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 $\sim2$. 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.(abridged)
Comment: 17 pages, 11 figures, accepted for publication in ApJ