Exploring the Cosmic Dawn with Subaru Telescope

Observational studies of z ∼> 6 galaxies are important to understand cosmic reionization and the early stage of galaxy formation. We present our recent results for z ∼> 6 galaxies found by Subaru surveys. The Lyα luminosity function (LF) of Ly α emitters (LAEs) evolves in Lyα luminosity from z = 5.7 to 6.6. This evolution of Lyα LF is likely explained by the reionization of the Universe at z ∼ 6, since the UV LF of LAEs does not change from z = 5.7 to 6.6. On the other hand, bright dropout galaxies show a significant deficit at z ∼ 6. The number density of dropouts continues to decrease probably up to z = 7 − 8. It may be a hint for the hierarchical mass assembly of galaxies. We then introduce our on-going studies for z ∼> 7 galaxies with Subaru/SuprimeCam and the new instrument, MOIRCS, which has unique capabilities in deep and wide-field near-infrared observations. These on-going studies will address the issues in reionization and galaxy formation with intrinsically-bright z ∼> 7 galaxies, which compliments the recent searches for high-z galaxies with gravitational lensing.