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arXiv · 1604.08590

Deep imaging of Eridanus II and its lone star cluster

D. Crnojević·D. J. Sand·D. Zaritsky·K. Spekkens·B. Willman·J. R. Hargis
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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$$280$ pc and is elongated ($\epsilon$$\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.

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D. Crnojević, D. J. Sand, D. Zaritsky, K. Spekkens, B. Willman, J. R. Hargis. 2016-04-28. Deep imaging of Eridanus II and its lone star cluster. https://doi.org/10.3847/2041-8205%2F824%2F1%2Fl14

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