Broadband photometry of 105 giant arcs: Redshift constraints and implications for giant arc statistics

Abstract

We measure the photometric properties of 105 giant arcs that were identified in systematic searches for galaxy-cluster-scale strong lenses in the Second Red-Sequence Cluster Survey and the Sloan Digital Sky Survey. The cluster lenses span 0.2 < zl < 1.2 in redshift, with a median . Using broadband color criteria we sort the entire arc sample into redshift bins based on u-g and g-r colors, and also r-z colors for the 90% of arcs that have z-band data. This analysis yields broad redshift constraints with 71+5- 4% of the arcs at z ≥ 1.0, 64+6- 4% at z ≥ 1.4, 56+5- 4% at z ≥ 1.9, and 21+4- 2% at z ≥ 2.7. The remaining 29+03- 5% have z < 1. The inferred median redshift is , in good agreement with a previous determination from a smaller sample of brighter arcs (g ≲ 22.5). This agreement confirms that zs = 2.0 0.1 is the typical redshift for giant arcs with g ≲ 24 that are produced by cluster-scale strong lenses and that there is no evidence for strong evolution in the redshift distribution of arcs over a wide range of g-band magnitudes (20 ≤ g ≤24). Establishing that half of all giant arcs are at z ≳ 2 contributes significantly toward relieving the tension between the number of arcs observed and the number expected in a ΛCDM cosmology, but there is considerable evidence to suggest that a discrepancy persists. Additionally, this work confirms that forthcoming large samples of giant arcs will supply the observational community with many magnified galaxies at z ≳ 2. © 2012 The American Astronomical Society. All rights reserved.