(Proposal ID) S17A-024

(PI) Yasuda, Naoki

(Proposal Title)
Probing Dark Energy with z>1 SNe Ia from HSC SSP Transient Survey

(Abstract)
Type Ia Supernova is an one of powerful probes to constrain the nature of dark 
energy through the detailed, accurate, and unbiased measurement of the 
expansion history of the Universe. The existing and on-going observations of 
z < 1 sample place strong constraints on rho_{DE}(z) out to z~1. At the 
redshift beyond z > 1, the current constraints have little statistical 
strength due to the lack of well-measured SNe Ia at this redshift. HSC is 
an unique instrument to effectively find SNe at this high redshift, and 
HSC SSP starts coordinated transient survey from the end of November 2016. 
In this transient survey which continues for 6 months, we expect to detect 
50-70 SNe Ia beyond z > 1. We propose here spectroscopic follow-up observation 
of SN+host galaxy detected by this HSC transient survey. The proposed 
observation ensures the high purity of selecting high-z SNe Ia to be followed 
by infrared camera (WFC3) on the HST for measuring accurate SN color. Our S16B 
proposal had been already accepted but the survey continues to S17A and this 
is the request for the continuing spectroscopy follow-up. In addition, we are 
awarded 46+50 HST orbits for the next 2 cycles (24 and 25). This proposed 
observation is critical for the success of the HSC+HST SNIa cosmology project.