Discovery of a Split Stellar Stream In the Periphery of the Small Magellanic Cloud

TL;DR

A new stellar stream named Sutlej was discovered near the Small Magellanic Cloud using Gaia data, characterized by its distinct structure, metallicity, and motion, suggesting it is not directly associated with the Magellanic Clouds.

Contribution

This paper reports the discovery and detailed characterization of the Sutlej stellar stream near the SMC, including its structure, composition, and kinematics, using Gaia DR3 data.

Findings

The stream consists of two parallel components separated by 2.5 degrees.

The stream's stars have a median metallicity of [M/H]=-1.8.

The tangential velocity of the stream is 214 km/s, indicating it is likely not associated with the Magellanic Clouds.

Abstract

I report the discovery of a stellar stream (Sutlej) using Gaia DR3 proper motions and XP metallicities located ~15 degrees north of the Small Magellanic Cloud (SMC). The stream is composed of two parallel linear components ("branches") approximately ~8 x 0.6 degrees in size and separated by 2.5 degrees. The stars have a mean proper motion of (pmra,pmdec)=(+0.08 mas/yr,-1.41 mas/yr) which is quite similar to the proper motion of stars on the western side of the SMC. The color magnitude diagram of the stream stars has a clear red giant branch, horizontal branch, and main sequence turnoff that is well-matched by a PARSEC isochrone of 10 Gyr, [Fe/H]=-1.8 at 32 kpc and a total stellar mass of ~33,000 Msun. The stream is spread out over an area of 9.6 square degrees and has a surface brightness of 32.5 mag/arcsec^2. The metallicity of the stream stars from Gaia XP spectra extend 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 compared to the values of 448 km/s for the Large Magellanic Cloud and 428 km/s 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 ~25 degrees which might indicate an important gravitational influence from the nearby Magellanic Clouds.