Gaia DR3 S3 stream candidates

To investigate the origin of S3, we evolved stream models in time-dependent and deforming Milky Way and LMC haloes, accounting for the dynamical effects of the Milky Way-LMC interaction. We identify 2177 S3 stream candidates with P>0.5 that satisfy the proper-motion polygon selection, from which we define a high-confidence subsample of 1542 new S3 stream candidates using a probability threshold P_cut_=0.8. We also provide a catalogue of 440 potential S3 red clump stars, which are particularly valuable targets for spectroscopic follow-up due to their well-defined luminosities and their ability to yield precise distance estimates.

Both the dynamical modelling and a comparison between the closest approach distances and velocities of S3 stars relative to the LMC escape velocity indicate that S3 is unlikely to originate from the LMC. Instead, S3 is best interpreted as a distant Milky Way stellar stream located at approximately 75kpc. S3 is therefore the most distant known extended Milky Way stellar stream, with a length of about 30 degrees and a thickness of 3 to 4 degrees, corresponding to a physical width of roughly 4 to 5kpc.

This makes S3 one of the thickest stellar streams discovered to date and a unique probe of the outer Milky Way halo and of the recent dynamical influence of the LMC.