We present the discovery of d1005+68 , a new faint dwarf galaxy in the M81 Group , using observations taken with the Subaru Hyper Suprime-Cam .
d1005+68 ’ s color-magnitude diagram is consistent with a distance of 3.98 _ { -0.43 } ^ { +0.39 } Mpc , establishing group membership .
We derive an absolute V -band magnitude , from stellar isochrone fitting , of M _ { V } = -7.94 _ { -0.50 } ^ { +0.38 } , with a half-light radius of r _ { h } = 188 _ { -41 } ^ { +39 } pc .
These place d1005+68 within the radius–luminosity locus of Local Group and M81 satellites and among the faintest confirmed satellites outside the Local Group .
Assuming an age of 12 Gyr , d1005+68 ’ s red giant branch is best fit by an isochrone of [ Fe/H ] = -1.90 \pm 0.24 .
It has a projected separation from nearby M81 satellite BK5N of only 5 kpc .
As this is well within BK5N ’ s virial radius , we speculate that d1005+68 may be a satellite of BK5N .
If confirmed , this would make d1005+68 one of the first detected satellites-of-a-satellite .