Abstract
We present the final results from our survey of luminous z similar to 5.5 quasars. This is the first systematic quasar survey focusing on quasars at z similar to 5.5, during the post-reionization epoch. It has been challenging to select quasars at 5.3 < z < 5.7 using conventional color selections, due to their similar optical colors to those of late-type stars, especially M dwarfs. We developed a new selection technique for z similar to 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 similar to 11,000 deg(2) 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 similar to 5.5 and M1450 < -26.2. Our result is consistent with the rapid decline of the quasar spatial density from z = 5 to 6, with k = -0.66 +/- 0.05 (rho(z) alpha 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.