The Andromeda Galaxy's Last Major Merger: Constraints from the survey of Planetary Nebulae
arXiv (Cornell University)(2023)
Abstract
The Andromeda galaxy (M 31) has experienced a tumultuous merger history as
evidenced by the many substructures present in its inner halo. We use planetary
nebulae (PNe) as chemodynamic tracers to shed light on the recent merger
history of M 31. We identify the older dynamically hotter thicker disc in M 31
and a distinct younger dynamically colder thin disc. The two discs are also
chemically distinct with the PN chemodynamics implying their formation in a
`wet' major merger (mass ratio 1:5) 2.5-4 Gyr ago. From comparison of PN
line-of-sight velocities in the inner halo substructures with predictions of a
major-merger model in M 31, we find that the same merger event that formed the
M 31 thick and thin disc is also responsible for forming these substructures.
We thereby obtain constraints on the recent formation history of M 31 and the
properties of its cannibalized satellite.
MoreTranslated text
Key words
planetary nebulae,andromeda galaxy,last major merger
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