Abstract
We present initial results from the first systematic survey of luminous
$z5.5$ quasars. Quasars at $z \sim$ 5.5, the post-reionization epoch, are
crucial tools to explore the evolution of intergalactic medium, quasar
evolution and the early super-massive black hole growth. However, it has been
very challenging to select quasars at redshifts 5.3 $z łe$ 5.7 using
conventional color selections, due to their similar optical colors to late-type
stars, especially M dwarfs, resulting in a glaring redshift gap in quasar
redshift distributions. We develop a new selection technique for $z \sim$ 5.5
quasars based on optical, near-IR and mid-IR photometric data from Sloan
Digital Sky Survey (SDSS), UKIRT InfraRed Deep Sky Surveys - Large Area Survey
(ULAS), VISTA Hemisphere Survey (VHS) and Wide field Infrared Survey Explorer
(WISE). From our pilot observations in SDSS-ULAS/VHS area, we have discovered
15 new quasars at 5.3 $z łe$ 5.7 and 6 new lower redshift quasars, with
SDSS z band magnitude brighter than 20.5. Including other two $z \sim$ 5.5
quasars already published in our previous work, we now construct an uniform
quasar sample at 5.3 $z łe$ 5.7 with 17 quasars in a $\sim$ 4800 square
degree survey area. For further application in a larger survey area, we apply
our selection pipeline to do a test selection by using the new wide field J
band photometric data from a preliminary version of the UKIRT Hemisphere Survey
(UHS). We successfully discover the first UHS selected $z \sim$ 5.5 quasar.
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