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We present the unexpected discovery of four ultra diffuse galaxies (UDGs) ina group environment. We recently identified seven extremely low surfacebrightness galaxies in the vicinity of the spiral galaxy M101, using data fromthe Dragonfly Telephoto Array. The galaxies have effective radii of $10"-38"$and central surface brightnesses of $25.6-27.7$ mag arcsec$^{-2}$ in g-band. Wesubsequently obtained follow-up observations with $HST$ to constrain thedistances to these galaxies. Four remain persistently unresolved even with thespatial resolution of $HST$/ACS, which implies distances of $D > 17.5$ Mpc. Weshow that the galaxies are most likely associated with a background group at$\sim 27$ Mpc containing the massive ellipticals NGC 5485 and NGC 5473. At thisdistance, the galaxies have sizes of $2.6-4.9$ kpc, and are classified as UDGs,similar to the populations that have been revealed in clusters such as Coma,Virgo and Fornax, yet even more diffuse. The discovery of four UDGs in a galaxygroup demonstrates that the UDG phenomenon is not exclusive to clusterenvironments. Furthermore, their morphologies seem less regular than those ofthe cluster populations, which may suggest a different formation mechanism orbe indicative of a threshold in surface density below which UDGs are unable tomaintain stability.

The Dragonfly Nearby Galaxies Survey. II. Ultra diffuse galaxies near the elliptical galaxy NGC 5485