Observations are important tools for us to access information on physical conditions of various astronomical objects. Photons from the Universe have a wide frequency range, each of which traces different spatial/energy scales in the Universe. In addition, recent cosmic-ray and gravitational wave observations opened up a new research field “multi-messenger astronomy”.

I conducted an optical observation towards galaxy clusters by using Subaru Telescope on Mauna Kea in Hawaii to constrain the scenarios of galaxy formation and star formation in galaxies. I also closely collaborate with observers to reveal the mechanisms of molecular cloud evolution and subsequent star formation by comparing their observational results with my supercomputer simulations and semi-analytic theories.