Research Byte

Published in the RSAA Lunations
Vol1 Issue1 1–29 February 2020

 Two major accretion epochs in Andromeda from two distinct populations of globular clusters.

 In this recently-published Nature paper (October 2019) we used globular clusters to trace the kinematics of Andromeda’s stellar halo. We found that classifying the clusters into two populations — one embedded in a heavily sub-structured halo component, and one belonging to a smoothly distributed component — also leads to a distinct kinematic separation. Both components exhibit strong rotation signatures, but oriented perpendicular to each other. This likely points to two major accretion epochs in Andromeda’s history, separated by billions of years. Surprisingly, the rotation axis for clusters from the ancient epoch is very closely aligned with the rotation axis for the mysterious plane of dwarf galaxies that encircles Andromeda. This may indicate large-scale accretion from a preferred direction in the local environment over cosmic history.

 Here’s the free version of the paper: https://arxiv.org/abs/1910.00808

Here’s the (very good) ABC News article: https://ab.co/3blzPhl 

And here’s the (mildly amusing) Daily Mail article: https://dailym.ai/2tCXNn6

 

 Dougal Mackey