南方基地知识库

High-redshift quasars are important tracers of structure and evolution in the early universe. However, they are very rare and difficult to find when using color selection because of contamination from late-type dwarfs. High-redshift quasar surveys based on only optical colors suffer from incompleteness and low identification efficiency, especially at z greater than or similar to 4.5. We have developed a new method to select 4.7 less than or similar to z less than or similar to 5.4 quasars with both high efficiency and completeness by combining optical and mid-IR Wide-field Infrared Survey Explorer (WISE) photometric data, and are conducting a luminous z similar to 5 quasar survey in the whole Sloan Digital Sky Survey (SDSS) footprint. We have spectroscopically observed 99 out of 110 candidates with z-band magnitudes brighter than 19.5, and 64 (64.6%) of them are quasars with redshifts of 4.4 less than or similar to z less than or similar to 5.5 and absolute magnitudes of -29 less than or similar to M-1450 less than or similar to -26.4. In addition, we also observed 14 fainter candidates selected with 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 similar to 36% of the number of known quasars at this redshift range. More importantly, our identifications doubled the number of quasars with M1450 < -27.5 at z > 4.5, which will set strong constraints on the bright end of the quasar luminosity function. We also expand our method to select quasars at z greater than or similar to 5.7. In this paper we report the discovery of four new luminous z greater than or similar to 5.7 quasars based on SDSS WISE selection.