paper

Deep imaging of Eridanus II and its lone star cluster

arXiv:1604.08590 · doi:10.3847/2041-8205/824/1/L14

Abstract

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 ( $I^µ$ $\sim$ $0.48$ ), 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.

7 pages, 4 figures; ApJL accepted