The giant arc statistics in the three-year Wilkinson Microwave Anisotropy Probe cosmological model

Abstract

Abstract We use high-resolution N-body simulations to investigate the optical depth of giant arcs with length-to-width ratios larger than 7.5 and 10 in the ‘standard’Λ cold dark matter (ΛCDM) model with σ8 = 0.9 and Ωm,0 = 0.3 and a model based on three-year Wilkinson Microwave Anisotropy Probe (WMAP) data. We find that, in dark-matter-only simulations, the lensing probability in the three-year WMAP model (with σ8 = 0.74 and Ωm,0 = 0.238) decreases by a factor of ∼6 compared with that in the ‘standard’Λ cold dark matter (ΛCDM) model. The effects of baryonic cooling, star formation and feedbacks are uncertain, but we argue that baryons will only increase the the lensing cross-section by a moderate factor, ∼2. We conclude that the low central value of σ8 and Ωm,0 preferred by the WMAP three-year data may be too low to be compatible with observations if the conventional assumptions of the background source population are correct.