On the incidence of strong gravitational lensing by clusters in the Las Campanas distant cluster survey

The observed incidence of strongly lensing clusters exceeds the predictions of a ACDM model by about a factor of 10. We revisit the observational side of this discrepancy by measuring the incidence of strong lensing in a subsample of clusters drawn from the Las Campanas Distant Cluster Survey (LCDCS). Among clusters with 0.5 ≤ z ≤ 0.7, the redshift range in which we focus our search, we find two strongly lensed systems within an effective search area of 69 deg². There is at least one other strongly lensed system in the LCDCS outside of this redshift range, where we are less complete. Over all redshifts, the ACDM model produces one large arc every 146 deg². Assuming Poisson statistics, the probability of finding three or more strongly lensing clusters in 69 deg² is 0.012. The lensing incidence within the LCDCS is in agreement with that derived from an X-ray-selected sample and what has been preliminarily presented from an independent optical cluster survey. The origin of the disagreement between theory and observations, which remains at least at the order-of-magnitude scale for the ACDM model, lies either in the concordance cosmological model, in the characteristics of the resulting cluster potentials, or in the adopted source population.