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High-redshift quasars are important tracers of structure and evolution in theearly universe. However, they are very rare and difficult to find when usingcolor selection because of contamination from late-type dwarfs. High-redshiftquasar surveys based on only optical colors suffer from incompleteness and lowidentification efficiency, especially at $z\gtrsim4.5$. We have developed a newmethod to select $4.7\lesssim z \lesssim 5.4$ quasars with both high efficiencyand completeness by combining optical and mid-IR Wide-field Infrared SurveyExplorer (WISE) photometric data, and are conducting a luminous $z\sim5$ quasarsurvey in the whole Sloan Digital Sky Survey (SDSS) footprint. We havespectroscopically observed 99 out of 110 candidates with $z$-band magnitudesbrighter than 19.5 and 64 (64.6\%) of them are quasars with redshifts of$4.4\lesssim z \lesssim 5.5$ and absolute magnitudes of $-29\lesssim M_{1450}\lesssim -26.4$. In addition, we also observed 14 fainter candidates selectedwith the same criteria and identified 8 (57.1\%) of them as quasars with$4.7<z<5.4$ . Among 72 newly identified quasars, 12 of them are at $5.2 < z <5.7$, which leads to an increase of $\sim$36\% of the number of known quasarsat this redshift range. More importantly, our identifications doubled thenumber of quasars with $M_{1450}<-27.5$ at $z>4.5$, which will set strongconstraints on the bright end of the quasar luminosity function. We also expandour method to select quasars at $z\gtrsim5.7$. In this paper we report thediscovery of four new luminous $z\gtrsim5.7$ quasars based on SDSS-WISEselection.

A survey of luminous high-redshift quasars with SDSS and WISE. I. target selection and optical spectroscopy