The GALAH Survey: No chemical evidence of an extragalactic origin for the Nyx stream

Daniel B. Zucker*, Jeffrey D. Simpson, Sarah L. Martell, Geraint F. Lewis, Andrew R. Casey, Yuan Sen Ting, Jonathan Horner, Thomas Nordlander, Rosemary F. G. Wyse, Tomaž Zwitter, Joss Bland-Hawthorn, Sven Buder, Martin Asplund, Gayandhi M. De Silva, Valentina D'Orazi, Ken C. Freeman, Michael R. Hayden, Janez Kos, Jane Lin, Karin LindKatharine J. Schlesinger, Sanjib Sharma, Dennis Stello

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)


The results from the ESA Gaia astrometric mission and deep photometric surveys have revolutionized our knowledge of the Milky Way. There are many ongoing efforts to search these data for stellar substructure to find evidence of individual accretion events that built up the Milky Way and its halo. One of these newly identified features, called Nyx, was announced as an accreted stellar stream traveling in the plane of the disk. Using a combination of elemental abundances and stellar parameters from the GALAH and Apache Point Observatory Galactic Evolution Experiment (APOGEE) surveys, we find that the abundances of the highest likelihood Nyx members are entirely consistent with membership of the thick disk, and inconsistent with a dwarf galaxy origin. We conclude that the postulated Nyx stream is most probably a high-velocity component of the Milky Way's thick disk. With the growing availability of large data sets including kinematics, stellar parameters, and detailed abundances, the probability of detecting chance associations increases, and hence new searches for substructure require confirmation across as many data dimensions as possible.

Original languageEnglish
Article numberL30
Pages (from-to)1-7
Number of pages7
JournalAstrophysical Journal Letters
Issue number2
Publication statusPublished - 10 May 2021


Dive into the research topics of 'The GALAH Survey: No chemical evidence of an extragalactic origin for the Nyx stream'. Together they form a unique fingerprint.

Cite this