Xue-Bing Wu, Wen-Wen Zuo, Qian Yang, Weimin Yi, Chenwei Yang, Wenjuan Liu, Peng Jiang, Xinwen Shu, Hongyan Zhou
Quasars with redshifts greater than four are rare, and can provide us important helps in probing the nature of the early universe. Here we report the discovery of six new quasars with $i$-band magnitudes brighter than 19.5 and redshifts between 2.4 and 4.6 from the spectroscopic observations made with the YFOSC instrument of the Lijiang 2.4m telescope in February, 2012. These six quasars are in the list of high redshift ($z>3.6$) quasar candidates selected by using our proposed J-K/i-Y criterion and the photometric redshift estimations from the SDSS optical and UKIDSS near-IR photometric data. Nine candidates were observed by YFOSC, and five among six new quasars were identified as $z>3.6$ quasars. One of the other three objects was identified as a star and the rest two were unidentified due to the lower signal-to-noise ratio of their spectra. This is the first time to discover quasars with redshifts greater than four with a telescope in China. Thanks to the Chinese Telescope Access Program (TAP), the redshift of 4.6 for one of these new quasars was confirmed by the MMT Red Channel spectroscopy. The continuum and emission line properties of these six quasars, as well as their central black hole masses and Eddington ratios, were obtained.
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http://arxiv.org/abs/1206.3611
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