THE SUBARU HIGH- z QUASAR SURVEY: DISCOVERY OF FAINT z ∼ 6 QUASARS

We present the discovery of one or two extremely faint z ~ 6 quasars in 6.5 deg[sup 2] utilizing a unique capability of the wide-field imaging of the Subaru/Suprime-Cam. The color selection can effectively isolate quasars at z ~ 6 from M/L/T dwarfs without the J-band photometry down to z[subR] < 24.0, which is 3.5 mag deeper than the Sloan Digital Sky Survey (SDSS). We derive the quasar luminosity function at z ~ 6 by combining our faint quasar sample with the bright quasar samples by SDSS and CFHQS. Including our data points invokes a higher number density in the faintest bin of the quasar luminosity function than the previous estimate employed. This suggests a steeper faint-end slope than lower z, though it is yet uncertain based on a small number of spectroscopically identified faint quasars, and several quasar candidates still remain to be diagnosed. This was found to still be insufficient for the required photon budget of re-ionization at z ~ 6.