We report on the detection in Sloan Digital Sky Survey data of a 63°-long tidal stream of stars, extending from Ursa Major to Cancer. The stream has no obvious association with the orbit of any known cluster or galaxy. The contrast of the detected stream is greatest when using a star count filter that is matched to the color-magnitude distribution of stars in M13, which suggests that the stars making up the stream are old and metal-poor. The visible portion of the stream is very narrow and about 8.5 kpc above the Galactic disk, suggesting that the progenitor is or was a globular cluster. While the surface density of the stream varies considerably along its length, its path on the sky is very smooth and uniform, showing no evidence of perturbations by large mass concentrations in the nearby halo. While definitive constraints cannot be established without radial velocity information, the stream's projected path and estimates of its distance suggest that we are observing the stream near the perigalacticon of its orbit.
The Astrophysical Journal
- Pub Date:
- May 2006
- Galaxy: Halo;
- Galaxy: Structure;
- Galaxy: Globular Clusters: General;
- 12 pages, 2 figures, accepted for publication in the Astrophysical Journal Letters. Updated to correspond to version accepted by ApJ