アブストラクト：
"Over the last decade, resolved star studies of nearby galaxies have led to the discovery of vast satellites and sub-structures. These components are naturally predicted in models of hierarchical galaxy assembly, and their observed properties place important constraints on the amount, nature, and time history of dwarf galaxy accretion to large galaxies. I present the results from the M81 mapping with HSC on Subaru Telescope. The resolved stellar photometry covering a projected radius of 120 kpc from M81 group centre enable us to reveal the extended halos of old RGB stars and the young intra-group population, and to identify a new satellite candidate in the survey footprint."