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

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Published 2007 January 19 © 2007. The American Astronomical Society. All rights reserved. Printed in U.S.A.
, , Citation M. J. Irwin et al 2007 ApJ 656 L13 DOI 10.1086/512183

1538-4357/656/1/L13

Abstract

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 ~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 ~200 Myr. There is a compact cloud of neutral hydrogen with mass ~105 M and radial velocity +35 km s-1 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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10.1086/512183