Collisions between galaxies create tidal artifacts of all sorts of shapes. This new work by Ivanna Escala has found conclusive evidence that Andromeda’s northeast, west, and southeast plateaus and the giant stellar stream are the result of a collision with another galaxy. Studying these tidal features can teach us how galaxies grow and change over time as they accumulate new material. Credit: NASA, ESA, Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University), K. Noll (STScI) and J. Westphal (Caltech) .
A detailed analysis of the composition and motion of more than 500 stars has revealed conclusive evidence of an ancient collision between Andromeda and a nearby galaxy. The findings, which improve our understanding of the events that shape galaxy evolution, were presented Monday by Carnegie’s Ivanna Escala at the American Astronomical Society meeting.
Galaxies grow by accreting material from nearby objects – other galaxies and dense clusters of stars called globular clusters – often following a catastrophic crash. And these events leave behind relics in the form of stellar associations that astronomers call tidal features. This may include elongated currents or arcing shells moving around the surviving galaxy. Studying these phenomena can help us understand the history of a galaxy and the forces that shaped its appearance and composition.
“The remnants of each crash can be identified by studying the motion of stars and their chemical compositions. Together, this information serves as a sort of fingerprint that identifies stars that have 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 plateau, which forms a sharp edge in the density of galaxy material.
“We have performed the first detailed characterization of the chemical composition and geometric motion of stars in this region of our neighboring galaxy, conclusively demonstrating that the NE shelf is a tidal shell composed primarily of debris resulting from a collision,” explained Escala.
The Andromeda Galaxy, also known as M-31. Credit: NASA / MSFC / Bureau of Meteoroid Environment / Bill Cook
Their work also demonstrates that the NE shelf is part of a multi-shell system with the western and southeastern shelves of the galaxy and that the material in these regions is consistent with that of the Andromeda giant starstream, linking all these tidal characteristics as potentially coming from the same source.
“Our results are consistent with modeling that predicts the Giant Stellar Stream to be the first loop of material in a collision and the NE shelf to be the second enclosing layer,” Escala concluded.
This level of analysis confirms predictions about Andromeda’s violent past and informs astronomers’ understanding of how matter accumulated by collisions shapes the surrounding features and evolutionary history of a galaxy.
Our Galaxy’s Most Recent Major Collision
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Tracing the Remnants of Andromeda’s Violent History (2022, June 13)
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