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Quasars with redshifts greater than 4 are rare, and can be used to probe thestructure and evolution of the early universe. Here we report the discovery ofsix new quasars with $i$-band magnitudes brighter than 19.5 and redshiftsbetween 2.4 and 4.6 from the YFOSC spectroscopy of the Lijiang 2.4m telescopein February, 2012. These quasars are in the list of $z>3.6$ quasar candidatesselected by using our proposed $J-K/i-Y$ criterion and the photometric redshiftestimations from the SDSS optical and UKIDSS near-IR photometric data. Ninecandidates were observed by YFOSC, and five among six new quasars wereidentified as $z>3.6$ quasars. One of the other three objects was identified asa star and the other two were unidentified due to the lower signal-to-noiseratio of their spectra. This is the first time that $z>4$ quasars have beendiscovered using a telescope in China. Thanks to the Chinese Telescope AccessProgram (TAP), the redshift of 4.6 for one of these quasars was confirmed bythe Multiple Mirror Telescope (MMT) Red Channel spectroscopy. The continuum andemission line properties of these six quasars, as well as their central blackhole masses and Eddington ratios, were obtained.

Discovery of six high-redshift quasars with the Lijiang 2.4m telescope and the Multiple Mirror Telescope