Substructure in Tidal Streams: Tributaries in the Anticenter Stream

We report on the detection in Sloan Digital Sky Survey data of at leastthree, roughly parallel components in a 65 degree-long stellar stream complexpreviously identified with the Anticenter or Monoceros Ring. The three-streamcomplex varies in width from 4 to 6 degrees along its length and appears to bemade up of two or more narrow substreams as well as a broader, diffusecomponent. The width and complexity of the stream indicate that the progenitorwas likely a dwarf galaxy of significant size and mass. The stream is 8.9 kpcdistant and is oriented almost perpendicularly to our line of sight. Thevisible portion of the stream does not pass near any known dwarf galaxies and apreliminary orbit does not point to any viable progenitor candidates. Orbitsfor the narrower substreams can be modeled with velocity offsets from the broadcomponent of about 8 km/s. We suggest that the broad component is likely to bethe remains of a dwarf galaxy, while the narrower streams constitute theremnants of dynamically distinct components which may have included a nativepopulation of globular clusters. While the color of the main sequence turn-offis not unlike that for the Monoceros Ring, neither the visible stream nor anyreasonable projection of its orbit passes through Monoceros or Canis Major, andwe conclude that this stream is probably unrelated to the overdensities foundin these regions.Comment: 11 pages, 4 figures, accepted for publication in ApJ Letter