The Galactic Halo's Contribution to Inner Galaxy Stellar Populations

Abstract: The metal-poor stars in the inner Galaxy are thought to be the oldest stars in our Galaxy. Therefore their chemodynamical properties can uniquely inform and constrain theories of early Milky Way formation and evolution. Although the metal-rich stars in the inner Galaxy participate in the Galactic bar and corresponding boxy/peanut-shaped (B/P) bulge, the dynamical structure of the metal-poor stars is highly debated. In this talk, I will discuss my work from the Chemodynamical Origins of Metal-Poor Bulge Stars (COMBS) survey, demonstrating that at least half of the metal-poor stars in the inner Galaxy are halo stars on orbits with apocenters > 3.5 kpc. As similar works have now found consistent results, the debate is now focused on the remaining stars that do stay confined to the inner regions of the Galaxy. Do these metal-poor stars have origins in an ancient disk component and participate in the B/P  bulge or are they part of a pressure-supported component like a classical bulge possibly formed from early galaxy mergers? Or are they consistent with the continuation of a simple power-law halo which would have its highest density in the inner regions of the Milky Way? I will discuss predictions for the minor-axis stellar density profile of the Milky Way from cosmological zoom-in simulations. Last, I will preview current work measuring the inner halo stellar density profile using Gaia DR3 data. 

This seminar is organised by the Ursa Minor research group and is open to all.