Dating the Gaia-Enceladus-Sausage Merger using Asteroseismology
During the Milky Way’s lifetime, it has merged with several dwarf galaxies. One of the largest mergers was with the galaxy know as Gaia-Enceladus-Sausage (GES). To fully understand the evolution and current structure of our Galaxy it is important to know when these mergers happened. Using asteroseismology in combination with spectroscopic and photometric measurements of solar-like oscillators we can determine the ages of the stars with great accuracy. In this talk, I present how we use Gaia eDR3 data to make a dynamical selection of red giant stars that once belonged to the GES galaxy. I also describe how we use asteroseismology from the Kepler and K2 mission along with chemical abundances from APOGEE and photometry from 2MASS to determine the ages of these GES stars. From these age determinations, we can constrain when the GES merger happened and thereby contribute to mapping out the evolutionary history of our Galaxy.