Discovery of a faint old stellar system at 150 kpc

We report the detection of a faint old stellar system at (alpha, delta)=(194 degrees 29, 34 degrees 32) (SDSS J1257+3419), based on the spatial distribution of bright red giant branch stars in the Sloan Digital Sky Survey Data Release 4. SDSS J1257+3419 has a half-light radius of 38 +/- 12 pc and an absolute integrated V magnitude of M-v= -4.8=(1.4)(-1.0) mag at a heliocentric distance of 150 +/- 15 kpc. A comparison between SDSS J1257+3419 and known Galactic halo objects suggests that SDSS J1257+3419 is either (1) a faint and small dwarf galaxy or (2) a faint and widely extended globular cluster. In the former case, SDSS J1257+3419 could represent an entity of a postulated subhalo of the Milky Way. Further photometric and dynamical study of this stellar system is vital to distinguish these possibilities.