Details

Autor(en) / Beteiligte

• Wang, Shuyu
• Necib, Lina
• Ji, Alexander P.
• Ou, Xiaowei
• Lisanti, Mariangela
• de los Reyes, Mithi A. C.
• Strom, Allison L.
• Truong, Mimi

Titel

High-resolution Chemical Abundances of the Nyx Stream

Ist Teil von

• The Astrophysical journal, 2023-10, Vol.955 (2), p.129

Ort / Verlag

Philadelphia: The American Astronomical Society

Erscheinungsjahr

2023

Link zum Volltext

Quelle

EZB Free E-Journals

Beschreibungen/Notizen

• Abstract 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.