NSF OIR Lab: Two Ancient Migration Events in Andromeda

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Two Ancient Migration Events in the Andromeda Galaxy
NSF National Optical-Infrared Astronomy Research Laboratory | 2019 Oct 02
Gemini Observatory | National Optical Astronomy Observatory

Dynamical footprints uncovered by galactic archaeologists in galaxy next door

The globular clusters studied (lower right insets), indicated by colored circles, are located in the outer halo of the Andromeda Galaxy, beyond the bright disk of the galaxy (upper left inset). The star clusters separate into two groups — those associated and unassociated with stellar streams — that have very different orbits, a result that points to two discrete migration events in the history of the galaxy. The color of each circle indicates the line-of-sight velocity of the corresponding star cluster. Credit: Australian National University/NSF’s National Optical-Infrared Astronomy Research Laboratory

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Astronomers have uncovered two historic events in which the Andromeda Galaxy underwent major changes to its structure. The findings shed light not only on the evolution and formation of the Andromeda Galaxy, but to our own Milky Way Galaxy as well. Two of the facilities in NSF's National Optical-Infrared Astronomy Research Laboratory, Kitt Peak National Observatory and the International Gemini Observatory, played critical roles in the research, now published in the latest issue of the journal Nature.

Large galaxies like the one we live in, the Milky Way, are believed to grow through repeated merging with smaller, dwarf galaxies. Gas and dwarf galaxies in the vast cosmic web follow the gravitational paths laid out by dark matter — traversing filaments, they migrate slowly toward collections of dark matter and assemble into large galaxies. As dwarf galaxies are pulled in by gravity, they are also pulled apart, leaving behind long trailing streams of stars and compact star clusters.

Astronomers have uncovered evidence for two major migration events in the history of our large galactic neighbor, the Andromeda Galaxy (also known as M31). The more recent migration event occurred a few billion years ago and the older event many billions of years before that. The evidence for the two events comes from “galactic archaeology,” the use of the motions and properties of stars and stellar clusters to reconstruct the formation and evolutionary history of galaxies. ...

The Violent History of the Big Galaxy Next Door
Australian National University | 2019 Oct 03

Revealed: The Violent Past of Andromeda
University of Sidney | 2019 Oct 03

Two Major Accretion Epochs in M31 from Two Distinct Populations of Globular Clusters ~ Dougal Mackey et al

• Nature 574(7776):69 (03 Oct 2019) DOI: 10.1038/s41586-019-1597-1
  arXiv.org > astro-ph > arXiv:1910.00808 > 02 Oct 2019