We present deep imaging of the most distant dwarf discovered by the Dark Energy Survey , Eridanus II ( Eri II ) .
Our Magellan/Megacam stellar photometry reaches \sim 3 mag deeper than previous work , and allows us to confirm the presence of a stellar cluster whose position is consistent with Eri II ’ s center .
This makes Eri II , at M _ { V } = -7.1 , the least luminous galaxy known to host a ( possibly central ) cluster .
The cluster is partially resolved , and at M _ { V } = -3.5 it accounts for \sim 4 \% of Eri II ’ s luminosity .
We derive updated structural parameters for Eri II , which has a half-light radius of \sim 280 pc and is elongated ( \epsilon \sim 0.48 ) , at a measured distance of D \sim 370 kpc .
The color-magnitude diagram displays a blue , extended horizontal branch , as well as a less populated red horizontal branch .
A central concentration of stars brighter than the old main sequence turnoff hints at a possible intermediate-age ( \sim 3 Gyr ) population ; alternatively , these sources could be blue straggler stars .
A deep Green Bank Telescope observation of Eri II reveals no associated atomic gas .