The Local Stellar Halo is Not Dominated by a Single Radial Merger Event

Thomas Donlon II*, Heidi Jo Newberg, Bokyoung Kim, Sebastien Lepine

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

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 σv ∼ 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.
Original languageEnglish
Article numberL16
Pages (from-to)1-6
Number of pages6
JournalAstrophysical Journal Letters
Issue number2
Publication statusPublished - 17 Jun 2022

Keywords / Materials (for Non-textual outputs)

  • astro-ph.GA


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