Nearby stellar substructures in the Galactic halo from DESI Milky Way Survey Year 1 Data Release

We report five nearby ($d_{\mathrm{helio}} < 5$ kpc) stellar substructures in the Galactic halo from a subset of 138 661 stars in the Dark Energy Spectroscopic Instrument (DESI) Milky Way Survey Year 1 Data Release. With an unsupervised clustering algorithm, HDBSCAN*, these substructures are independently identified in Integrals of Motion ($E_{\rm tot}$, $L_{\rm z}$, $\log {J_r}$, $\log {J_z}$) space and Galactocentric cylindrical velocity space ($V_{R}$, $V_{\phi }$, $V_{z}$). We associate all identified clusters with known nearby substructures (Helmi streams, M18-Cand10/MMH-1, Sequoia, Antaeus, and ED-2) previously reported in various studies. With metallicities precisely measured by DESI, we confirm that the Helmi streams, M18-Cand10, and ED-2 are chemically distinct from local halo stars. We have characterized the chemodynamic properties of each dynamic group, including their metallicity dispersions, to associate them with their progenitor types (globular cluster or dwarf galaxy). Our approach for searching substructures with HDBSCAN* reliably detects real substructures in the Galactic halo, suggesting that applying the same method can lead to the discovery of new substructures in future DESI data. With more stars from future DESI data releases and improved astrometry from the upcoming Gaia Data Release 4, we will have a more detailed blueprint of the Galactic halo, offering a significant improvement in our understanding of the formation and evolutionary history of the Milky Way Galaxy.. Authors: Kim, Bokyoung [Institute for Astronomy, University of Edinburgh , Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ ,] (ORCID:0000000289991108); Koposov, Sergey E [Institute for Astronomy, University of Edinburgh , Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ ,; Institute of Astronomy, University of Cambridge , Madingley Road, Cambridge CB3 0HA ,] (ORCID:000000032644135X); Li, Ting S [University of Toronto Department of Astronomy & Astrophysics, , Toronto, ON M5S 3H4 ,] (ORCID:0000000291106163); Lilleengen, Sophia [Durham University Institute for Computational Cosmology, Department of Physics, , South Road, Durham DH1 3LE ,] (ORCID:000000019046691X); Cooper, Andrew P [National Tsing Hua University Institute of Astronomy and Department of Physics, , 101 Kuang-Fu Road Section 2, Hsinchu 30013 ,; Center for Informatics and Computation in Astronomy, NTHU , 101 Kuang-Fu Rd. Section 2, Hsinchu 30013 ,] (ORCID:000000018274158X). DOE Contract: 89243024CSC000002; AC02-05CH11231; SC0019193. Subjects: dynamics; galaxies; halo; kinematics; solar neighborhood; stars