Dwarf satellite galaxies are a key probe of dark matter and of galaxy formation on small scales and of the dark matter halo masses of their central galaxies .
They have very low surface brightness , which makes it difficult to identify and study them outside of the Local Group .
We used a low surface brightness-optimized telescope , the Dragonfly Telephoto Array , to search for dwarf galaxies in the field of the massive spiral galaxy M101 .
We identify seven large , low surface brightness objects in this field , with effective radii of 10 - 30 arcseconds and central surface brightnesses of \mu _ { g } \sim 25.5 - 27.5 mag arcsec ^ { -2 } .
Given their large apparent sizes and low surface brightnesses , these objects would likely be missed by standard galaxy searches in deep fields .
Assuming the galaxies are dwarf satellites of M101 , their absolute magnitudes are in the range -11.6 \lesssim M _ { V } \lesssim - 9.3 and their effective radii are 350 pc - 1.3 kpc .
Their radial surface brightness profiles are well fit by Sersic profiles with a very low Sersic index ( n \sim 0.3 - 0.7 ) .
The properties of the sample are similar to those of well-studied dwarf galaxies in the Local Group , such as Sextans I and Phoenix .
Distance measurements are required to determine whether these galaxies are in fact associated with M101 or are in its foreground or background .