Prof. Alex Ji, University of Chicago)

"Dwarf Galaxy Archaeology in the Gaia Era"

Abstract: The Milky Way's satellite dwarf galaxies are powerful probes of many important astrophysical processes. Their kinematics provide insights into galactic dynamics and the nature of dark matter, while their chemical compositions preserve a history of early galaxy formation and nucleosynthesis. Recently, all-sky astrometry from the Gaia satellite has enabled the discovery and characterization of dwarf galaxies at different stages of tidal disruption. These new galaxies lie at the extremes of dwarf galaxy parameter space, whether in their structural properties or their star formation histories. In this talk, I will show how spectroscopic observations of the kinematics and chemistry of these newly discovered dwarf galaxies can provide crucial insights into galactic dynamics and nucleosynthesis. I will present a recent kinematic study of the extremely diffuse dwarf galaxy Antlia II that shows it is in the early stages of tidal disruption. The kinematics of Antlia II also clearly show that the Milky Way reference frame has been perturbed by the Large Magellanic Cloud. I will also highlight how two completely disrupted dwarf galaxies contribute to increasingly clear evidence that the rapid neutron-capture process requires both prompt and delayed sources to explain the diverse chemical evolution histories of dwarf galaxies.

Bio: Alex Ji is an Assistant Professor of Astronomy and Astrophysics at the University of Chicago. He did his BS in Physics and MS in Statistics at Stanford, then obtained his PhD at MIT. He was a Hubble and Carnegie Fellow at the Observatories of the Carnegie Institution for Science from 2017-2021. His research focuses on observational near-field cosmology, using stellar spectroscopy to study the first stars and galaxies, nuclear astrophysics, dwarf galaxy formation and evolution, and local constraints on dark matter.