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The faint and ultrafaint dwarf galaxies in the Local Group form theobservational bedrock upon which our understanding of small-scale cosmologyrests. In order to understand whether this insight generalizes, it isimperative to use resolved-star techniques to discover similarly faintsatellites in nearby galaxy groups. We describe our search for ultrafaintgalaxies in the M81 group using deep ground-based resolved-star data sets fromSubaru's Hyper Suprime-Cam. We present one new ultrafaint dwarf galaxy in theM81 group and identify five additional extremely low surface brightnesscandidate ultrafaint dwarfs that reach deep into the ultrafaint regime to $M_V\sim -6$ (similar to current limits for Andromeda satellites). Thesecandidates' luminosities and sizes are similar to known Local Group dwarfgalaxies Tucana B, Canes Venatici I, Hercules, and Bo\"otes I. Most of thesecandidates are likely to be real, based on tests of our techniques on blankfields. Intriguingly, all of these candidates are spatially clustered aroundNGC 3077, which is itself an M81 group satellite in an advanced state of tidaldisruption. This is somewhat surprising, as M81 itself and its largestsatellite M82 are both substantially more massive than NGC 3077 and by virtueof their greater masses, would have been expected to host as many or moreultrafaint candidates. These results lend considerable support to the idea thatsatellites of satellites are an important contribution to the growth ofsatellite populations around Milky Way-mass galaxies.

Ultrafaint Dwarf Galaxy Candidates in the M81 Group: Signatures of Group Accretion