Filling in the Quasar Redshift Gap at z?～?5.5. II. A Complete Survey of Luminous Quasars in the Post-reionization Universe

摘要

We present the final results from our survey of luminous z?~?5.5 quasars. This is the first systematic quasar survey focusing on quasars at z?~?5.5, during the post-reionization epoch. It has been challenging to select quasars at 5.3?z?z?~?5.5 quasars based on optical, near-infrared (IR), and mid-IR photometry, using data from the Sloan Digital Sky Survey (SDSS), PanSTARR1 (PS1), the UKIRT Infrared Deep Sky Surveys–Large Area Survey, the UKIRT Hemisphere Survey, the VISTA Hemisphere Survey, and the Wide Field Infrared Survey Explorer, covering ~11,000 deg2 of high galactic latitude sky. In this paper, we present the discovery of 15 new quasars at 5.22?≤?z?≤?5.78. Together with results from Yang et al., our survey provides a complete, flux-limited sample of 31 quasars at 5.3?≤?z?≤?5.7. We measure the quasar spatial density at z?~?5.5 and M 1450?z?=?5 to 6, with k?=??0.66?±?0.05 (ρ(z)?∝?10 kz ). In addition, we present a new survey using optical colors only from the full PS1 area for luminous quasars at z?=?5.0–5.5, which is beyond the SDSS footprint, and report the preliminary results from this survey, including 51 new quasars discovered at 4.61?≤?z?≤?5.71.