Lunch talk on Oct. 21th, 2019
Dynamical Relics of The Ancient Galactic Halo
Speaker: Zhen Yuan (SHAO)
Venue: Room 2111, SWIFAR Building
Time: 12:00 PM, Monday, 21th October, 2019
We search for dynamical substructures in the LAMOST DR3 very metal-poor (VMP) star catalog. After cross-matching with Gaia DR2, there are ∼ 3300 VMP stars with available high-quality astrometric information that have halo-like kinematics. We apply a method based on self-organizing maps, StarGO, to find groups clustered in the 4D space of orbital energy and angular momentum. We are able to recover all the existing substructures such as Gaia-Sausage, Sequoia, and the Helmi Stream. There are also a few new substructures discovered. More interestingly, we found one VMP dominated substructure Rg5 is dynamically associated with two highly r-process-enhanced stars with [Fe/H] ∼ −3. This finding indicates that its progenitor might be an ultra-faint dwarf galaxy that has experienced r-process enrichment from neutron star mergers. This study has taken the first steps in finding dynamical associations between disrupted dwarf galaxies and r-process-enhanced stars, which is crucial for studying their birth environments. This helps us understand the nucleosynthetic events and chemical evolution in UFDs and other dwarf galaxies in the early universe. The great advantage of studying debris in the nearby halo is that high-resolution spectroscopic observations are much more readily obtainable, so we expect this field of activity to have a rich future in the coming decades.