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 ∼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 MV=−7.1, the least luminous galaxy known to host a (possibly central) cluster. The cluster is partially resolved, and at MV=−3.5 it accounts for ∼4% of Eri II's luminosity. We derive updated structural parameters for Eri II, which has a half-light radius of ∼280 pc and is elongated (ϵ∼0.48), at a measured distance of D∼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 (∼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.
@article{arxiv.1604.08590,
title = {Deep imaging of Eridanus II and its lone star cluster},
author = {D. Crnojević and D. J. Sand and D. Zaritsky and K. Spekkens and B. Willman and J. R. Hargis},
journal= {arXiv preprint arXiv:1604.08590},
year = {2016}
}