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Discovery of an Unusual Dwarf Galaxy in the Outskirts of the Milky Way

M. J. Irwin·V. Belokurov·N. W. Evans·E. V. Ryan-Weber·J. T. A. de Jong·S. Koposov·D. B. Zucker·S. T. Hodgkin·G. Gilmore·P. Prema·L. Hebb·A. Begum·M. Fellhauer·P. C. Hewett·R. C. Kennicutt, Jr.·M. I. Wilkinson·D. M. Bramich·S. Vidrih·H. -W. Rix·T. C. Beers·J. C. Barentine·H. Brewington·M. Harvanek·J. Krzesinski·D. Long·A. Nitta·S. A. Snedden
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Abstract

In this Letter, we announce the discovery of a new dwarf galaxy, Leo T, in the Local Group. It was found as a stellar overdensity in the Sloan Digital Sky Survey Data Release 5 (SDSS DR5). The color-magnitude diagram of Leo T shows two well-defined features, which we interpret as a red giant branch and a sequence of young, massive stars. As judged from fits to the color-magnitude diagram, it lies at a distance of about 420 kpc and has an intermediate-age stellar population with a metallicity of [Fe/H]= -1.6, together with a young population of blue stars of age of 200 Myr. There is a compact cloud of neutral hydrogen with mass roughly 10^5 solar masses and radial velocity 35 km/s coincident with the object visible in the HIPASS channel maps. Leo T is the smallest, lowest luminosity galaxy found to date with recent star-formation. It appears to be a transition object similar to, but much lower luminosity than, the Phoenix dwarf.

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M. J. Irwin, V. Belokurov, N. W. Evans, E. V. Ryan-Weber, J. T. A. de Jong, S. Koposov, D. B. Zucker, S. T. Hodgkin, G. Gilmore, P. Prema, L. Hebb, A. Begum, M. Fellhauer, P. C. Hewett, R. C. Kennicutt, Jr., M. I. Wilkinson, D. M. Bramich, S. Vidrih, H. -W. Rix, T. C. Beers, J. C. Barentine, H. Brewington, M. Harvanek, J. Krzesinski, D. Long, A. Nitta, S. A. Snedden. 2007-01-05. Discovery of an Unusual Dwarf Galaxy in the Outskirts of the Milky Way. https://doi.org/10.1086/512183

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