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We present the first results of a wide-field mapping survey of the M81 groupconducted with Hyper Suprime-Cam on the Subaru Telescope. Our deep photometryreaches $\sim2$ magnitudes below the tip of the red giant branch (RGB) andreveals the spatial distribution of both old and young stars over an area of$\sim 100\times115$ kpc at the distance of M81. The young stars ($\sim30-160$Myr old) closely follow the neutral hydrogen distribution and can be found in astellar stream between M81 and NGC\,3077 and in numerous outlying stellarassociations, including the known concentrations of Arp's Loop, Holmberg\,IX,an arc in the halo of M82, BK3N, and the Garland. Many of these groupings donot have counterparts in the RGB maps, suggesting they may be genuinely youngsystems. Our survey also reveals for the first time the very extended ($\geq2\times \rm{R_{25}}$) halos of RGB stars around M81, M82 and NGC\,3077, as wellas faint tidal streams that link these systems. The halos of M82 and NGC\,3077exhibit highly disturbed morphologies, presumably a consequence of the recentgravitational encounter and their ongoing disruption. While the halos of M81,NGC\,3077 and the inner halo of M82 have the similar $(g-i)_{0}$ colors, theouter halo of M82 is significantly bluer indicating it is more metal-poor.Remarkably, our deep panoramic view of the M81 group demonstrates that thecomplexity long-known to be present in HI is equally matched in the low surfacebrightness stellar component.

A Hyper Suprime-Cam View of the Interacting Galaxies of the M81 Group