  The study of outer halo globular cluster (GC) populations can give insight
into galaxy merging, globular cluster accretion and the origin of GCs. We use
archival Subaru Hyper Suprime-Cam (HSC) data in concert with space-based GALEX,
IRAC and Gaia EDR3 data to select candidate Globular clusters (GCs) in the
outer halo of the M81 group for confirmation and future study. We use a small
sample of previously-discovered GCs to tune our selection criteria, finding
that bright already-known GCs in the M81 group have sizes that are typically
slightly larger than the Subaru PSF in our fields. In the optical bands, GCs
appear to have colours that are only slightly different from stars. The
inclusion of archival IRAC data yields dramatic improvements in colour
separation, as the long wavelength baseline aids somewhat in the separation
from stars and clearly separates GCs from many compact background galaxies. We
show that some previously spectroscopically-identified GCs in the M81 group are
instead foreground stars or background galaxies. GCs close to M82 have radial
velocities suggesting that they fell into the M81 group along with M82. The
overall M81 GC luminosity function is similar to the Milky Way and M31. M81's
outer halo GCs are similar to the Milky Way in their metallicities and numbers,
and much less numerous than M31's more metal-rich outer halo GC population.
These properties reflect differences in the three galaxies' merger histories,
highlighting the possibility of using outer halo GCs to trace merger history in
larger samples of galaxies.
