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.

欧空局盖亚天体测量任务和深度光度测量的结果彻底改变了我们对银河系的认识。有许多正在进行的努力在这些数据中搜索恒星的子结构，以寻找形成银河系及其光晕的单个吸积事件的证据。这些新发现的特征之一，称为 Nyx，被宣布为一条在盘面传播的吸积恒星流。使用来自 GALAH 和阿帕奇点天文台银河演化实验 (APOGEE) 调查的元素丰度和恒星参数的组合，我们发现可能性最大的 Nyx 成员的丰度与厚盘的成员完全一致，而与矮星不一致银河起源。我们得出结论，假设的 Nyx 流很可能是银河系厚盘的高速成分。随着包括运动学、恒星参数和详细丰度在内的大型数据集的可用性不断增加，检测机会关联的可能性增加，因此对子结构的新搜索需要在尽可能多的数据维度上进行确认。