Presentation #407.05 in the session “Star Clusters: Galactic & Extragalactic”.
With the combination of large data-producing observatories and the introduction of modern statistical and machine learning techniques needed to interpret and mine these data, the past decade has witnessed great advances in the study of Milky Way stellar populations. After applying one such unsupervised clustering algorithm called HDBSCAN to the Gaia DR2 astrometric catalog, Kounkel & Covey (2019) identified over a thousand structures, including a number of large-scale filaments, within a kpc of the Sun. We focus on one of these structures, Theia 456, which spans 20 degrees and 175 pc. Despite its size, we argue that the stars in Theia 456 are co-eval (based on photometrically derived rotation periods), co-metallicity (based on LAMOST spectra) and have a common dynamical origin (based on Gaia astrometry). We summarize the characteristics of Theia 456, and discuss its relevance in the context of other newly identified substructures within the Milky Way.