Photometry and Spectroscopy of i-drop Galaxies: Possible Detection of A Proto-cluster at z=6

We discovered 30 candidate galaxies are clustering in a small ~200 Mpc² region at z = 6 with 5σ local density excess in a wide 876 arcmin² field. Four of them were spectroscopically identified as z = 5.9-6.0 Lyα emitters (~34 Mpc in line-of-sight). This structure is comparable to z = 4.8 and 5.7 galaxy proto-clusters previously found. Since the other candidates are likely to be real galaxies due to low sample contamination, the overdensity can be a z~6 proto-cluster.