2005/03/31 by Beth Willman, Julianne J. Dalcanton, David Martinez-Delgado +18 · 4 citations
Physics and Astronomy · #Absolute magnitude #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Dwarf galaxy #Dwarf galaxy problem #Dwarf spheroidal galaxy #Galaxies: Formation, Evolution, Phenomena #Galaxy #Interacting galaxy #Local Group #Luminosity #Magnitude (astronomy) #Milky Way #Physics #Star formation #Stellar population #Stellar, planetary, and galactic studies #Surface brightness #astro-ph
paper · pdf · doi:10.1086/431760
published as Astrophys.J.626:L85-L88,2005 · Replaced with ApJL accepted version. Includes some additional details, corrected references, and minor changes to Figure 4
arxiv created 2005/05/11 · openalex publication_date 2005/05/24 · arxiv updated 2012/08/27 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
In this Letter, we report the discovery of a new dwarf satellite to the Milky Way, located at (α 2000 , δ 2000 ) = (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 M V = -6.75 and r 1/2 = 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.