Program: GS-2008A-Q-16

Reionization was the transition of the intergalactic medium from neutral to predominantly ionized by redshift z~6, caused by ionizing radiation from the earliest stars and quasars. Quasars at redshifts z>5.5 are useful probes of reionization, since their high ultraviolet luminosities enable absorption studies of the IGM. However, our present understanding of reionization is in part limited by cosmic variance: different lines of sight show different IGM optical depths at the same redshift. Many more high-redshift quasar sightlines are needed to overcome cosmic variance. We have identified six z>5.5 quasar candidates using near-IR imaging of 164 objects with extremely red R-z' colors from the 90-square-degree Red-sequence Cluster Survey. These quasar candidates deviate from the (R-z',z'-J) colors expected for late-type dwarf stars at significance levels >=3.5 sigma. We request identification spectroscopy of three A-semester candidates, one using GMOS-N and two using GMOS-S. Any quasars discovered will be targets for extensive future followup.