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, M. I. Wilkinson, D. M. Bramich, S. Vidrih, H. W. Rix, T. C. BeersJ. C. Barentine, H. Brewington, M. Harvanek, J. Krzesinski, D. Long, A. Nitta, S. A. Snedden

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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.

Original languageEnglish
JournalAstrophysical Journal
Issue number1 II
Publication statusPublished - 10 Feb 2007
Externally publishedYes



  • Galaxies: dwarf
  • Galaxies: individual (Leo)
  • Local group

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Irwin, M. J., Belokurov, V., Evans, N. W., Ryan-Weber, E. V., De Jong, J. T. A., Koposov, S., Zucker, D. B., Hodgkin, S. T., Gilmore, G., Prema, P., Hebb, L., Begum, A., Fellhauer, M., Hewett, P. C., Kennicutt, R. C., Wilkinson, M. I., Bramich, D. M., Vidrih, S., Rix, H. W., ... Snedden, S. A. (2007). Discovery of an unusual dwarf galaxy in the outskirts of the milky way. Astrophysical Journal, 656(1 II).