Discovery of a split stellar stream in the periphery of the small magellanic cloud

ABSTRACT I report the discovery of a stellar stream (Sutlej) using Gaia DR3 (third data release) proper motions and XP metallicities located 15° north of the Small Magellanic Cloud (SMC). The stream is composed of two parallel linear components (‘branches’) approximately 8° × 0. 6° in size and separated by 2. 5°. The stars have a mean proper motion of (ₑ₀, ₃₄₂. ) = (+0. 08 mas yr−1, −1. 41 mas yr−1), which is quite similar to the proper motion of stars on the western side of the SMC. The colour–magnitude diagram of the stream stars has a clear red giant branch, horizontal branch, and main-sequence turn-off that are well matched by a parsec isochrone of 10 Gyr, Fe/H = −1. 8 at 32 kpc, and a total stellar mass of 33 000 M. The stream is spread out over an area of 9. 6 deg2 and has a surface brightness of 32. 5 mag arcsec−2. The metallicity of the stream stars from Gaia XP spectra extends over -2. 5 M/H -1. 0 with a median of M/H = −1. 8. The tangential velocity of the stream stars is 214 km s−1 compared to the values of 448 km s−1 for the Large Magellanic Cloud and 428 km s−1 for the SMC. While the radial velocity of the stream is not yet known, a comparison of the space velocities using a range of assumed radial velocities shows that the stream is unlikely to be associated with the Magellanic Clouds. The tangential velocity vector is misaligned with the stream by nearly 90°, which might indicate an important gravitational influence from the nearby Magellanic Clouds.