Variations of the Stellar Mass Function in the Milky Way Halo

Abstract:

I will show that the low-mass stellar mass function in the Milky Way halo using a clean sample of metal-poor main-sequence stars from Gaia DR3 BP/RP (XP) spectra within 1 kpc. Combining probabilistic kinematic halo selection with XP-based [Fe/H] calibrated to SDSS-V/APOGEE, and a forward model with effective volumes, we find that below 0.5 solar mass the halo MF changes strongly with metallicity: it is bottom-light at [Fe/H] ≲ –1.7 but becomes bottom-heavy and even steeper than a Kroupa IMF by [Fe/H] ≃ –1.2. These results show that the Galactic low-mass mass function is not universal, with variations in the metal-poor regime.

Speaker: 
Dr. Jiadong Li
Place: 
KIAA Shuqi meeting room
Time: 
Tuesday, January 6, 2026 - 3:30PM to Tuesday, January 6, 2026 - 4:30PM
Biography: 
Dr Jiadong Li is a postdoctoral researcher at the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany working with Professor Hans-Walter Rix. His research focuses on using statistical methods and AI to exploit large spectroscopic and astrometric surveys (SDSS-V/APOGEE, Gaia, LAMOST, CSST) to characterise binary star populations and constrain both the low-mass initial mass function and the formation pathways of binary systems, with a particular emphasis on low-mass stars and white dwarf binaries in the Milky Way. Before joining MPIA, he obtained his Ph.D in 2023 from NAOC, CAS.