Accurate Measurements of the Expansion of the Universe with imaging and spectroscopic observations of type Ia Supernovae

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The main purpose of this research project is to carry out imaging and spectroscopic observations of type la supernovae to measure cosmological expansion of the universe. We successfully found and measured distant supernovae with international collaboration programs, Supernova Cosmology Project and Sloan Digital Sky Survey.We found about 40 distant supernovae, 15 of which are type Ia supernovae. Some of those were found with Suprime-Cam, and some of those were found with Hubble Space Telescope. We carried out follow-up observations with Subaru and other large telescopes. We also found and observed nearby supernovae. Sloan Digital Sky Survey (SDSS) Supernova project so far found about 300 nearby supernovae, and we took more than 50 spectra with Subaru. Supernova data we have obtained are unique and will be able to give new constraints for cosmological models, although the analysis is still underway.Another activity of this research program was to develop a new imaging spectrograph for cosmology. We successfully build a 15-color band simultaneous imager. We have successfully carried out commissioning observations at 1.5-m Kanata telescope, Higashi Hiroshima Astronomical Observatory, Hiroshima University. Although no supernova observations have been made, the instrument is working well. This kind of instruments enable us to take spectroscopic information as well as imaging information for cosmological expansion measurements, and we developed basic techniques and knowledge through current instrumentation.We also studied cosmological expansion with the SDSS galaxy survey. SDSS galaxy distributions with Cosmic Microwave Background fluctuation measurements gave new constraints of cosmological parameters.