A Genetic approach to constraining the assembly of the Milky Way

Ted Mackereth (CITA)

June 14, 2021

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Abstract: The galaxy population in the universe is immutably linked to its cosmology. The characteristics of galaxies are genetic traits which are set, in a large part, by the DNA defined by density fluctuations in the early universe, which govern the eventual mass assembly of galaxies. Large scale surveys in the Milky Way such as Gaia, APOGEE and GALAH, among others, have revealed new and intriguing traits of the Milky Way. One such example is the clear bi-modality in alpha-element abundances relative to Iron at fixed Iron abundance, which exhibits itself throughout the disc of the Galaxy. Many recent works have focused on understanding and characterising this feature, and have shown that it is likely one of the most important features of the Milky Way to be understood, if we are to fully characterise its formation and evolution. Here, I will propose that the [alpha/Fe] bimodality in the Milky Way may be directly connected to its history of mass assembly. I will demonstrate, using genetically modified zoom-in cosmological simulations which vary the assembly history of a Milky Way-like galaxy whilst holding all other conditions fixed, that this is a good predictor of a galaxy’s stellar population structure in the [alpha/Fe] plane. This has far-reaching implications for understanding the Milky Way and the physics that lead to its formation, but also provides a compelling motivation to search for and characterise this feature in the external galaxy population.