Giant Arc Statistics and Cosmological Parameters

We study with semi-analytical methods the statistics of pronounced arcs caused by lensing of galaxies by foreground galaxy clusters. For the number density and redshift distribution of rich clusters we use Press-Schechter theory, normalized on the basis of empirical data. For the background sources we make use of observational results in the Hubble Deep Field. We present results for three different lens models, in particular for the universal profile suggested by Navarro, Frenk and White. Our primary concern is the dependence of the expected statistics on the cosmological parameters, ΩM , ΩΛ. The theoretical estimates are compared with the cluster arcs survey EMSS, and the resulting constraints in the Ω-plane are presented. In spite of considerable theoretical an observational uncertainties a low-density universe is favored. Degeneracy curves for the optical depth and likelihood regions for the arc statistics in the Ω-plane depend only weakly on the cosmological constant.