A curious Milky Way satellite in Ursa Major
- Zucker, D. B.
- Belokurov, V.
- Evans, N. W.
- Kleyna, J. T.
- Irwin, M. J.
- Wilkinson, M. I.
- Fellhauer, M.
- Bramich, D. M.
- Gilmore, G.
- Newberg, H. J.
- Yanny, B.
- Smith, J. A.
- Hewett, P. C.
- Bell, E. F.
- Rix, H. W.
- Gnedin, O. Y.
- Vidrih, S.
- Wyse, R. F. G.
- Willman, B.
- Grebel, E. K.
- Schneider, D. P.
- Beers, T. C.
- Kniazev, A. Y.
- Barentine, J. C.
- Brewington, H.
- Brinkmann, J.
- Harvanek, M.
- Kleinman, S. J.
- Krzesinski, J.
- Long, D.
- Nitta, A.
- Snedden, S. A.
DOIAbstract
In this Letter, we study a localized stellar overdensity in the constellation of Ursa Major, first identified in Sloan Digital Sky Survey (SDSS) data and subsequently followed up with Subaru imaging. Its color-magnitude diagram (CMD) shows a well-defined subgiant branch, main sequence, and turnoff, from which we estimate a distance of ~30 kpc and a projected size of ~250×125 pc2. The CMD suggests a composite population with some range in metallicity and/or age. Based on its extent and stellar population, we argue that this is a previously unknown satellite galaxy of the Milky Way, hereby named Ursa Major II (UMa II) after its constellation. Using SDSS data, we find an absolute magnitude of MV~-3.8, which would make it the faintest known sat...
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