The Milky Way -- An Immigrant Story

Speaker: Rohan Naidu (MIT) In Person and zoom 

Zoom info: https://stanford.zoom.us/j/98604058568

Galaxies like our Milky Way are predicted to grow by assimilating smaller, immigrant galaxies. The outer reaches of our Galaxy -- the stellar halo -- are predicted to be the melting pot for stars that were born elsewhere, but now call the Milky Way their home. Despite being scattered across the Galaxy, immigrant stars retain memory of their common origin that may be accessed via their shared chemistry and dynamics. The long-held aspiration of tracing every halo star to a distinct accreted galaxy has only recently become possible thanks to the Gaia astrometric mission. In this talk I will share highlights from my recently completed Magellan/MagE survey which, for the first time, has constrained orbits of individual stars out to 150 kpc. I will present a comprehensive inventory of our Galaxy, mapping debris from various known as well as previously undiscovered dwarf galaxies. I will discuss two key opportunities arising from such surveys: (i) star-by-star access to the stellar chemistry of ``high-redshift” galaxies, since the star-formation in these ancient systems was abruptly truncated when they were assimilated by our Galaxy; (ii) reconstructing the detailed dark matter distribution of the Milky Way as a sum of a now well-known series of mergers. In only five years, the number of massive (>million solar masses) dwarfs discovered in the stellar halo has exceeded the classical Milky Way satellites of comparable size -- I will discuss how the coming few years with surveys such as DESI and LSST promise to be a remarkably transformative one for astronomy at the edge of the Galaxy.