Tracing the remnants of Andromeda’s violent history
A detailed analysis of the composition and motion of more than 500 stars has provided compelling evidence of an ancient collision between Andromeda and a neighboring galaxy. The findings, which improve our understanding of the events that shape the evolution of galaxies, were presented Monday by Ivanna Escala of Carnegie at the meeting of the American Astronomical Society.
Galaxies grow by gobbling up 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 remnants in the form of stellar associations that astronomers call tidal features. These could be elongated streams or arc-shaped shells moving around the surviving galaxy. Studying these phenomena can help us understand the history of a galaxy and the forces that determined its appearance and composition.
“The remains of any crash can be identified by studying the motion of the stars and their chemical makeup. Together, this information serves as a fingerprint that identifies stars that joined a galaxy in a collision,” Escala explains.
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 the 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 ridge 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, convincingly demonstrating that the NE plateau is a tidal shell composed mainly of debris from the aftermath of a collision.” explains Escala.
Their work also shows that the NE plateau is part of a multi-shell system that includes the western and southeastern shelves of the galaxy and that the material in these regions is consistent with that of Andromeda’s Giant Stellar Stream, linking all of these tidal features. if possible from the same source.
“Our results are in line with modeling that predicted that the Giant Stellar Stream is the first material loop of a collision and the NE shelf is enveloping the second layer,” Escala concluded.
This level of analysis confirms predictions about Andromeda’s violent past and informs astronomers’ understanding of how collisional accretion shapes a galaxy’s surrounding features and evolutionary history.
Our galaxy’s most recent major collision
Quote: Tracing the Remnants of Andromeda’s Violent History (2022, June 13) retrieved June 13, 2022 from https://phys.org/news/2022-06-remnants-andromeda-violent-history.html
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