IMS High-z Quasar Survey - Faint z~6 Quasar Candidates in IMS Fields

Over the last decade, more than 50 quasars have been discovered at redshift about 6 when reionization of the universe occurred. However, most of them are luminous quasars (zAB < 21 mag), implying that such a biased quasar sample, which cannot represent the entire population of quasars at z~6, is not enough to understand the properties of quasars in the early universe. Recently, we have been performing the Infrared Medium-deep Survey (IMS), a moderately wide (120 deg2) and deep (JAB ~ 22.5 - 23 mag) near-infrared imaging survey. Combining this with the optical (ugriz) imaging data from the CFHT Legacy Survey (CFHTLS), we have identified more than 10 faint quasar candidates at z~6 in the IMS field by using multiple color selection criteria. From now on, we will perform spectroscopic confirmations of these faint quasar candidates with IMACS on the Magellan Baade Telescope at Las Campanas Observatory and GMOS on the Gemini South Telescope at Gemini Observatory. The confirmed quasars will be used to constrain the faint-end slope of the quasar luminosity function at z~6 and calculate the ratio of quasar ionizing flux to required flux for reionization of the universe. Moreover, these confirmed quasars will be followed up with near-infrared spectroscopy to determine their black hole masses and Eddington ratios to check the rapidness of their growth.