The formation of diverse stellar halos around Milky Way galaxies

ABSTRACT

The diffuse stellar halo surrounding galaxies provides a unique window into their formation, preserving signatures of past merger events several billion years after they occur. Recent advances in low-surface-brightness imaging have revealed an extensive diversity in extragalactic halos around disc galaxies, while data releases from the Gaia satellite allow us to unravel the Milky-Way’s history from its halo stars to an unprecedented accuracy. Interpreting these findings, to constrain our understanding of hierarchical galaxy formation, however requires us to accurately quantify how the interplay between each galaxy’s stochastic, cosmological merger history and internal non-linear, astrophysics shape its final stellar halo observables. In this talk, I will present a new approach to tackle this challenge using “genetically-modified” cosmological simulations. I will show how they allow us to disentangle how different merger scenarios and galaxy formation models distinctly contribute to the build-up of the diffuse stellar halos around Milky-Way-like galaxies, and provide a framework for interpreting Galactic data and constrain the Milky Way's history in a fully cosmological context.