Discovery of the Magellanic Stellar Stream Out to 100 kpc

Abstract

The Magellanic Stream (MS)—an enormous ribbon of gas spanning 140° of the southern sky trailing the Magellanic Clouds—has been exquisitely mapped in the five decades since its discovery. However, despite concerted efforts, no stellar counterpart to the MS has been conclusively identified. This stellar stream would reveal the distance and 6D kinematics of the MS, constraining its formation and the past orbital history of the Clouds. We have been conducting a spectroscopic survey of the most distant and luminous red giant stars in the Galactic outskirts. From this data set, we have discovered a prominent population of 13 stars matching the extreme angular momentum of the Clouds, spanning up to 100° along the MS at distances of 60–120 kpc. Furthermore, these kinematically selected stars lie along an [α/Fe]-deficient track in chemical space from −2.5 < [Fe/H] <− 0.5, consistent with their formation in the Clouds themselves. We identify these stars as high-confidence members of the Magellanic Stellar Stream. Half of these stars are metal-rich and closely follow the gaseous MS, whereas the other half are more scattered and metal-poor. We argue that the metal-rich stream is the recently formed tidal counterpart to the MS, and we speculate that the metal-poor population was thrown out of the SMC outskirts during an earlier interaction between the Clouds. The Magellanic Stellar Stream provides a strong set of constraints—distances, 6D kinematics, and birth locations—that will guide future simulations toward unveiling the detailed history of the Clouds.

Identifying H i Emission and UV Absorber Associations near the Magellanic Stream

“…The ram pressure forces exerted on the LMC and SMC as the galaxies travel through the MWʼs CGM may also contribute to the origin and present-day appearance of the MS (Salem et al 2015;Tepper-García et al 2015). Recent observational evidence on the existence of a Magellanic corona (Lucchini et al 2020;Krishnarao et al 2022, hereafter K22), a Magellanic stellar stream (Chandra et al 2023), and additional energetic processes near the Galactic center (Bland-Hawthorn et al 2013;Barger et al 2017;Fox et al 2020) further complicates the interpretation of the gaseous multiphase structure in the vicinity of the MS.…”