Large-Separation Lensed Quasars in the SDSS

The existence of lensed quasars with splitting angles larger than 7'' has been predicted on the basis of the cold dark matter model. We searched for these large-separation lensed quasars from the spectroscopically classified ∼40,000 quasars obtained by the Sloan Digital Sky Survey (SDSS), and succeeded in discovering the first lensed quasar by a cluster of galaxies, SDSS J1004+4112: It consists of four images, and the maximum separation is 14.62''. Here we describe the discovery and the follow-up observations of this system, as well as the latest results of the large-separation lens search in the SDSS. We also present the new statistical model which fully incorporates non-sphericity of dark halos, and compare the theoretical predictions with the SDSS results.