Tracing the remnants of Andromedas violent history Galaxies grow by accreting material from nearby objects—other galaxies and dense clumps of stars called globular clusters—often in the aftermath of a catastrophic crash. And these events leave behind relics in the form of stellar associations that astronomers call tidal features. This can include elongated streams or arcing shells moving around the surviving galaxy. Studying these phenomena can help us understand a galaxy's history and the forces that shaped its appearance and makeup."The remnants of each crash can be identified by studying the movement of the stars and their chemical compositions. Together this information serves as a kind of fingerprint that identifies stars that joined a galaxy in a collision," Escala explained.
She and her collaborators—Karoline Gilbert and Mark Fardal of the Space Telescope Science Institute, Puragra Guhathakurta of UC Santa Cruz, Robyn Sanderson of the University of Pennsylvania, Jason Kalirai of Johns Hopkins Applied Physics Laboratory, and Bahram Mobasher of UC Riverside—studied 556 red giant branch stars in a physical feature of Andromeda called the Northeast shelf, which forms a sharp ledge in the density of the galaxy's material."We performed the first detailed characterization of the chemical composition and geometric motion of the stars in this region of our neighboring galaxy, demonstrating conclusively that the NE shelf is a tidal shell predominately composed of debris from the aftermath of a collision," Escala explained. | |
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