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A Recent Major Radial Merger Leaves Shells in the Milky Way

Published onAug 03, 2020
A Recent Major Radial Merger Leaves Shells in the Milky Way

Radial collisions between galaxies create shell structure. We identify shell structure in the Milky Way for the first time, and claim that these shells are associated with the Virgo Radial Merger. Comparison to N-body simulations show that the observed shell structures are relatively unmixed, and therefore occurred recently (within the last 5 Gyr). Additional timing arguments pinpoint a collision 2.4 Gyr ago between the progenitor of these shells and the Milky Way. Previous work suggests that the Virgo Radial Merger and the Gaia Sausage/Gaia-Enceladus Merger are identical — however, the Gaia Sausage Merger is thought to have occurred 8-11 Gyr ago. Either the Virgo Radial Merger and the Gaia Sausage are different structures, or the Gaia Sausage is younger than previously thought.


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