The Simultaneous Globular Cluster and Dwarf Galaxy Origins of the Jhelum Stellar Stream

The characterization of stellar streams reveals key information about the formation of the Milky Way and the nature of dark matter. Jhelum is one such stellar stream, that is unique in that multiple distinct components have been detected, generating much discussion about the possible origins of this stream. We report a comprehensive characterization and member list of the Jhelum using new line-of-sight velocity and metallicity measurements from the Southern Stellar Stream Spectroscopic Survey (S5) and proper motions from Gaia DR3. Using Gaussian mixture modeling, we identify stream members based on their radial velocities, metallicities, and proper motions. We also create an updated member list with hundreds more stars than previous literature, and report the radial velocity and proper motions along each section of the stream. We confirm the presence of two kinematically distinct components in Jhelum, and find the two-stream component model is preferred to alternative models, such as a traditional one-component model or a newly reported three-component model. Additionally, our findings for velocity and metallicity dispersions are consistent with a globular cluster progenitor for one stream component and a dwarf galaxy progenitor for the other. This suggests that a dwarf galaxy with a globular cluster companion began their infall into the Milky Way and were tidally stripped together. Additionally, preliminary results reveal that another stellar stream, Indus, might also share this unique structure. We discuss further implications of these findings that reveal a new formation mechanism that provides insight into the Milky Way’s history.