PHYS/ASTR Colloquium: "Galactic Archeology with Low-Mass Stars and Brown Dwarfs: Prospects with Large-Scale Surveys" - Dr. Christian Aganze (Postdoc, Stanford U.)

San Francisco State University

Physics & Astronomy Colloquium Series

Monday, October 30, 2023

3:30 PM, Thornton Hall 411

Dr. Christian Aganze (Postdoc, Stanford U.) 

Galactic Archeology with Low-Mass Stars and Brown Dwarfs: Prospects with Large-Scale Surveys

Ultracool dwarfs (UCDs) are low-temperature stars and brown dwarfs with <0.1 solar masses. These objects make up at least 20% of all stars in the Milky Way, and they have long lifetimes (>1 trillion years). Brown dwarfs do not fuse hydrogen, and they cool down with time. This cooling provides an age dependence that can be exploited to characterize many Galactic environments (e.g. globular clusters, halo, and young clusters). Additionally, the spectra of UCDs are characterized by strong molecular features sensitive to chemical abundance effects, and UCDs preserve the initial chemistry of their progenitor molecular clouds. As such, UCDs serve as unique probes of the Milky Way System's structure, formation, and evolution. However, because of their intrinsically low luminosities, UCD samples have been limited to the local volume (d<100 pc) and have remained under-utilized in galactic archeology studies. Deep imaging and spectroscopic surveys, particularly with space-based telescopes, provide an opportunity to find distant brown dwarfs out to >1 kpc. This talk will present my work on finding distant ultracool dwarfs in two Hubble Space Telescope parallel surveys, extending to ~2 kpc. With this sample, I measured population ages as a function of spectral class. I confirmed that thin disk L dwarfs are younger than late-M dwarfs due to brown dwarf cooling. I also apply this modeling techniqueto predict that the next generation of deep and wide-field observatories, including JWST, the Nancy Grace Roman Telescope, the Vera Rubin Observatory, Euclid, and SPHEReX, will uncover millions of UCDs throughout various environments in the Galaxy, opening a new era for understanding the history of the Milky Way.