Key points are not available for this paper at this time.
We report the discovery of SDSSJ1049+5103, an overdensity of resolved blue stars at (\₂₀₀₀, \₂₀₀₀) = (162. 343, 51. 051). This object appears to be an old, metal-poor stellar system at a distance of 45\ 10 kpc, with a half-light radius of 23\ 10 pc and an absolute magnitude of MV = -3. 0^+2. 0-₀. ₇. One star that is likely associated with this companion has an SDSS spectrum confirming it as a blue horizontal branch star at 48 kpc. The color-magnitude diagram of SDSSJ1049+5103 contains few, if any, horizontal or red giant branch stars, similar to the anomalously faint globular cluster AM 4. The size and luminosity of SDSSJ1049+5103 places it at the intersection of the size-luminosity relationship followed by known globular clusters and that followed by Milky Way dwarf spheroidals. If SDSSJ1049+5103 is a globular cluster, then its properties are consistent with those of a globular cluster undergoing tidal disruption and with the established trend that the largest radius Galactic globular clusters are all in the outer halo. However, the five known globular clusters with similarly faint absolute magnitudes all have half-mass radii that are smaller than SDSSJ1049+5103 by a factor of \ 5. If it is a dwarf spheroidal, then it is the smallest and faintest yet known by more than an order of magnitude. The true nature of this new system is therefore ambiguous. One might expect the halo to contain numerous examples of such diffuse clusters. However, a simple friends-of-friends search for similar overdensities detected all 11 known globulars closer than 50 kpc in the SDSS area and this new object, but yielded no other clear cut candidates.
Willman et al. (Fri,) studied this question.