Detection of a 60°-long Dwarf Galaxy Debris Stream

Abstract

We report on a 60 degree-long stream of stars, extending from Ursa Major to Sextans, in the Sloan Digital Sky Survey. The stream is approximately 2 degrees wide and is clearly distinct from the northern tidal arm of the Sagittarius dwarf galaxy. The apparent width of the stream suggests a progenitor with a size and mass similar to that of a dwarf galaxy. The stream is about 21 kpc distant and appears to be oriented almost perpendicular to our line of sight. The visible portion of the stream does not pass near any known dwarf galaxies, though we cannot rule out that the stream may form the inner part of a known dwarf galaxy's orbit. The most likely explanation is that the stream constitutes the remains a dwarf galaxy that has been completely disrupted at some point in the past. We also briefly report on the discovery of a diminutive Galactic satellite which lies near the projected path of the new stream, but is unlikely to be related to it.