SDSS binary quasars at high redshift. I.

This paper describes the first systematic survey to discover high-redshift binary quasars. Using color-selection and photometric redshift techniques, we searched 8142deg^2^ of Sloan Digital Sky Survey imaging data for binary quasar candidates, and confirmed them with follow-up spectroscopy.

Our sample of 27 high-redshift binaries (24 of them new discoveries) at redshifts 2.9<z<4.3 with proper transverse separations 10kpc<R_T_<650kpc increases the number of such objects known by an order of magnitude. Eight members of this sample are very close pairs with R_T_<100kpc, and of these close systems four are at z>3.5. The completeness and efficiency of our well-defined selection algorithm are quantified using simulated photometry and we find that our sample is ~50% complete.