Open group seminar: Rohan Naidu (Harvard)

2:00–3:00 pm ERC 517

 Rohan Naidu (Harvard) "Unraveling the Galactic Stellar Halo with the H3 Survey"

The Milky Way has assimilated smaller, immigrant galaxies throughout its history. Its outer reaches (the stellar halo) are a melting pot for stars that were born elsewhere, but now call the MW their home. Despite being scattered across the Galaxy, accreted stars retain memory of their common origin that may be accessed via their shared chemistry and dynamics. In this talk I will present results from the ongoing H3 Survey -- the first dedicated halo survey in the Gaia era (150+ nights on the 6.5m MMT, 150k+ spectra of distant stars). I will present a comprehensive anatomy of our Galaxy out to 50 kpc, charting debris from various known and newly discovered mergers. This inventory of immigrant galaxies has opened up two exciting lines of inquiry: (i) these systems provide convenient, star-by-star access to the stellar chemistry of "high-z” galaxies at a resolution and scale inaccessible even to JWST; (ii) realistic models of the MW accounting for its detailed merger history are now possible -- I will argue that the last major merger at z~2 induced a ~30 degree tilt in the Milky Way’s dark matter halo with respect to the disk that remarkably persists to this day, requiring us to revisit virtually every conclusion drawn about the Galaxy assuming axisymmetry.

Event Type


Dec 2