This is a continuation of S23A program for which we were awarded 2 nights, but we lost one for bad seeing and the other for ToO. In S23B, we wish to request 1 night to compensate S23A program. We would like to complete a spectroscopic follow-up of the last HSC-HST observed Type Ia supernova (SNIa) host galaxies. SNIa is one of the most powerful probes to constrain the nature of dark energy. In addition to HSC SSP Transient survey, our sister projects (long term AGN, Superluminous SNe survey) added new 206 SNe in 2021 survey. In total, we have 669 SNeIa candidates including 217 SNeIa at z>1 (photo-z), a factor of six improvement. We have sent the best 36 supernovae to the Hubble Space Telescope (HST) for IR follow-up so that we can perform accurate SN color measurement. Through our international collaboration (Keck, Gemini, VLT, GTC, AAT and DESI), we have collected 357 spec-z. However 227 SNeIa remain photo-z, they cannot be placed on the Hubble Diagram for cosmological analysis. This proposed observation is critical to achieve the most precise measurement of dark energy. The remaining high-z host galaxies are very faint (24.0-24.5th mag in i-band) that are beyond reach of DESI/AAT. Our SNeIa data set would remain unique and competitive for years.
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