We report the discovery of two new globular clusters in the remote halos of M81 and M82 in the M81 Group based on the Hubble Space Telescope archive images .
They are brighter than typical globular clusters ( M _ { V } = -9.34 mag for GC-1 and M _ { V } = -10.51 mag for GC-2 ) , and much larger than known globular clusters with similar luminosity in the Milky Way Galaxy and M81 .
Radial surface brightness profiles for GC-1 and GC-2 do not show any feature for tidal truncation in the outer part .
They are located much farther from either of M81 and M82 in the sky , compared with previously known star clusters in these galaxies .
Color-magnitude diagrams of resolved stars in each cluster show a well-defined red giant branch ( RGB ) , indicating that they are metal-poor and old .
We derive a low metallicity with [ Fe/H ] \approx - 2.3 and an old age \sim 14 Gyr for GC-2 from the analysis of the absorption lines in its spectrum in the Sloan Digital Sky Survey in comparison with the simple stellar population models .
The I -band magnitude of the tip of the RGB for GC-2 is 0.26 mag fainter than that for the halo stars in the same field , showing that GC-2 is \sim 400 kpc behind the M81 halo along our line of sight .
The deprojected distance to GC-2 from M81 is much larger than any other known globular clusters in the local universe .
This shows that GC-2 is the most isolated globular cluster in the local universe .