A new Milky Way dwarf galaxy in URSA major

Beth Willman, Julianne J. Dalcanton, David Martinez-Delgado, Andrew A. West, Michael R. Blanton, David W. Hogg, J. C. Barentine, Howard J. Brewington, Michael Harvanek, S. J. Kleinman, Jurek Krzesinski, Dan Long, Eric H. Neilsen, Atsuko Nitta, Stephanie A. Snedden

    Research output: Contribution to journalArticlepeer-review


    In this Letter, we report the discovery of a new dwarf satellite to the Milky Way, located at (α2000, δ2000) = (158°.72, 51°.92) in the constellation of Ursa Major. This object was detected as an overdensity of red, resolved stars in Sloan Digital Sky Survey data. The color-magnitude diagram of the Ursa Major dwarf looks remarkably similar to that of Sextans, the lowest surface brightness Milky Way companion known, but with approximately an order of magnitude fewer stars. Deeper follow-up imaging confirms that this object has an old and metal-poor stellar population and is ∼100 kpc away. We roughly estimate MV = -6.75 and r1/2 = 250 pc for this dwarf. Its luminosity is several times fainter than the faintest known Milky Way dwarf. However, its physical size is typical for dwarf spheroidal galaxies. Even though its absolute magnitude and size are presently quite uncertain, Ursa Major is likely the lowest luminosity and lowest surface brightness galaxy yet known.

    Original languageEnglish (US)
    Pages (from-to)L85-L88
    JournalAstrophysical Journal
    Issue number2 II
    StatePublished - Jun 20 2005


    • Galaxies: dwarf
    • Local Group

    ASJC Scopus subject areas

    • Astronomy and Astrophysics
    • Space and Planetary Science


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