The Detection and Statistics of Giant Arcs Behind CLASH Clusters
  We developed an algorithm to find and characterize gravitationally lensed
galaxies (arcs) to perform a comparison of the observed and simulated arc
abundance. Observations are from the Cluster Lensing And Supernova survey with
Hubble (CLASH). Simulated CLASH images are created using the MOKA package and
also clusters selected from the high resolution, hydrodynamical simulations,
MUSIC, over the same mass and redshift range as the CLASH sample. The
algorithm' s arc elongation accuracy, completeness and false positive rate are
determined and used to compute an estimate of the true arc abundance. We derive
a lensing efficiency of $4 \pm 1$ arcs (with length $\ge 6"$ and
length-to-width ratio $\ge 7$) per cluster for the X-ray selected CLASH sample,
$4 \pm 1$ arcs per cluster for the MOKA simulated sample and $3 \pm 1$ arcs per
cluster for the MUSIC simulated sample. The observed and simulated arc
statistics are in full agreement. We measure the photometric redshifts of all
detected arcs and find a median redshift $z_s = 1.9$ with 33% of the detected
arcs having $z_s > 3$. We find that the arc abundance does not depend strongly
on the source redshift distribution but is sensitive to the mass distribution
of the dark matter halos (e.g. the $c-M$ relation). Our results show that
consistency between the observed and simulated distributions of lensed arc
sizes and axial ratios can be achieved by using cluster-lensing simulations
that are carefully matched to the selection criteria used in the observations.
