Abstract
We report the discovery of 15 quasars and bright galaxies at $5.7 < z < 6.9$.
This is the initial result from the Subaru High-$z$ Exploration of
Low-Luminosity Quasars (SHELLQs) project, which exploits the exquisite
multi-band imaging data produced by the Subaru Hyper Suprime-Cam (HSC)
Strategic Program survey. The candidate selection is performed by combining
several photometric approaches including a Bayesian probabilistic algorithm to
reject stars and dwarfs. The spectroscopic identification was carried out with
the Gran Telescopio Canarias and the Subaru Telescope for the first 80 deg$^2$
of the survey footprint. The success rate of our photometric selection is quite
high, approaching 100 % at the brighter magnitudes ($z_AB < 23.5$ mag).
Our selection also recovered all the known high-$z$ quasars on the HSC images.
Among the 15 discovered objects, six are likely quasars, while the other six
with interstellar absorption lines and in some cases narrow emission lines are
likely bright Lyman-break galaxies. The remaining three objects have weak
continua and very strong and narrow Ly $\alpha$ lines, which may be excited by
ultraviolet light from both young stars and quasars. These results indicate
that we are starting to see the steep rise of the luminosity function of $z \ge
6$ galaxies, compared to that of quasars, at magnitudes fainter than $M_\rm
1450 -22$ mag or $z_AB 24$ mag. Follow-up studies of the
discovered objects as well as further survey observations are ongoing.
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