High-resolution Chemical Abundances of the Nyx Stream

Nyx is a nearby, prograde, and high-eccentricity stellar stream physically contained in the thick disk, but its origin is unknown. Nyx could be the remnant of a disrupted dwarf galaxy, in which case the associated dark matter substructure could affect terrestrial dark matter direct-detection experim...

Full description

Saved in:
Bibliographic Details
Published in:The Astrophysical journal 2023-10, Vol.955 (2), p.129
Main Authors: Wang, Shuyu, Necib, Lina, Ji, Alexander P., Ou, Xiaowei, Lisanti, Mariangela, de los Reyes, Mithi A. C., Strom, Allison L., Truong, Mimi
Format: Article
Language:English
Subjects:
Abundance
ASTRONOMY AND ASTROPHYSICS
Astrophysics
Chemical analysis
Dark matter
Dwarf galaxies
Galaxy mergers & collisions
High resolution
Iron
Metallicity
Milky Way
Milky Way formation
Solar neighborhood
Spectroscopy
Stars
Stars & galaxies
Stellar abundances
Stellar kinematics
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:Nyx is a nearby, prograde, and high-eccentricity stellar stream physically contained in the thick disk, but its origin is unknown. Nyx could be the remnant of a disrupted dwarf galaxy, in which case the associated dark matter substructure could affect terrestrial dark matter direct-detection experiments. Alternatively, Nyx could be a signature of the Milky Way’s disk formation and evolution. To determine the origin of Nyx, we obtained high-resolution spectroscopy of 34 Nyx stars using Keck/HIRES and Magellan/MIKE. A differential chemical abundance analysis shows that most Nyx stars reside in a metal-rich ([Fe/H] > −1) high- α component that is chemically indistinguishable from the thick disk. This rules out the originally suggested scenario that Nyx is the remnant of a single massive dwarf galaxy merger. However, we also identify 5 substantially more metal-poor stars ([Fe/H] ∼ −2.0) whose chemical abundances are similar to those of the metal-weak thick disk. It remains unclear how stars that are chemically identical to the thick disk can be on such prograde, high-eccentricity orbits. We suggest two most likely scenarios: that Nyx is the result of an early minor dwarf galaxy merger, or that it is a record of the early spin-up of the Milky Way disk—although neither perfectly reproduces the chemodynamic observations. The most likely formation scenarios suggest that future spectroscopic surveys should find Nyx-like structures outside of the solar neighborhood.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/acec4d