Subaru Hyper Suprime Cam Survey of the Andromeda Halo

Masashi Chiba

We present a deep and wide-field photometric survey of the Andromeda halousing Hyper Suprime Cam (HSC) mounted on Subaru. HSC is the upgraded prime focuscamera after Suprime-Cam, having a field of view of 1.77 square degree(1.5 degree in diameter), namely about 10 times larger than that ofSuprime-Cam. This camera will thus offer us great opportunities to exploreunique and legacy surveys for the Andromeda halo, as well as for otherGalactic Archaeology science cases. We have carried out intensive surveyprograms for the Andromeda halo reaching a depth of 27.4 mag and 26.4 mag in gand i bands, respectively, which allows us to map out faint halo stars and derivetheir distribution in a color-magnitude diagram (CMD). In particular, based onthe characteristic stellar distribution in a CMD such as the horizontal branch (HB),red clump (RC) and red-giant-branch bump (RGBb), we succeed to determinethe line-of-sight distance distribution of the Northwest Stellar Streamin comparison with other field halo stars in Andromeda for the first time.These data of HB, RC and RGBb of the stellar stream are also combined withthe population properties of brighter RGB stars, which are distinguishedfrom the contamination of foreground Milky Way dwarf stars usinga narrow-band filter, NB515. The analysis of these combined data allows usto derive the age and metallicity of the stellar stream as well as those ofother field halo stars, which will thus set important constraints on the natureof a progenitor dwarf galaxy as the origin of the stream. We will also presentour further observing plan including spectroscopic follow-up studiesbased on Prime Focus Spectrograph (PFS) to be mounted on Subaru.