The Local Stellar Halo is Not Dominated by a Single Radial Merger Event
Abstract
We use halo dwarf stars with photometrically determined metallicities that are located within 2 kpc of the Sun to identify local halo substructure. The kinematic properties of these stars do not indicate a single, dominant radial merger event (RME). The retrograde Virgo Radial Merger (VRM) component has [Fe/H] = -1.7. A second, nonrotating RME component we name Nereus is identified with [Fe/H] = -2.1 and has similar energy to the VRM. We identify a possible third RME, which we name Cronus, that is corotating with the disk, has lower energy than the VRM, and has [Fe/H] = -1.2. We identify the Nyx Stream in the data. In addition to these substructures, we observe metal-poor halo stars ([Fe/H] ~ -2.0 and σ v ~ 180 km s-1) and a disk/Splash component with lower rotational velocity than the disk and lower metallicity than typically associated with the Splash. An additional excess of halo stars with low velocity and metallicity of [Fe/H] = -1.5 could be associated with the shell of a lower-energy RME or indicate that lower-energy halo stars have higher metallicity. Stars that comprise the "Gaia Sausage" velocity structure are a combination of the components identified in this work.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 2022
- DOI:
- 10.3847/2041-8213/ac7531
- arXiv:
- arXiv:2110.11465
- Bibcode:
- 2022ApJ...932L..16D
- Keywords:
-
- Milky Way Galaxy;
- Galaxy mergers;
- Galaxy accretion;
- Milky Way dynamics;
- 1054;
- 608;
- 575;
- 1051;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- doi:10.3847/2041-8213/ac7531