LAMOST DR3 very metal-poor stars of the Galactic halo

The very retrograde substructure Rg5 found previously by Myeong+ (2018MNRAS.478.5449M) is also retrieved. We report six new DTGs with highly retrograde orbits, two with very prograde orbits, and 12 with polar orbits. By mapping other data sets (APOGEE halo stars, and catalogs of r-process-enhanced and carbon-enhanced metal-poor [CEMP] stars) onto the trained neuron map, we can associate stars with detailed chemical abundances with the DTGs and look for associations with chemically peculiar stars.

The highly eccentric Gaia Sausage groups contain representatives of both debris from the satellite itself (which is {alpha}-poor) and the Splashed Disk, sent up into eccentric halo orbits from the encounter (and which is {alpha}-rich). The new prograde substructures also appear to be associated with the Splashed Disk. The DTGs belonging to the Gaia Sausage host two relatively metal-rich r-II stars and six CEMP stars in different subclasses, consistent with the idea that the Gaia Sausage progenitor is a massive dwarf galaxy.

Rg5 is dynamically associated with two highly r-process-enhanced stars with [Fe/H]~-3. This finding indicates that its progenitor might be an ultrafaint dwarf galaxy that has experienced r-process enrichment from neutron star mergers.