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

Bokyoung Kim; Sergey E. Koposov; Ting S. Li; Sophia Lilleengen; Andrew P. Cooper; Andreia Carrillo; Monica Valluri; Alexander H. Riley; Jiwon Jesse Han; Jessica Nicole Aguilar; Steven Ahlen; Leandro Beraldo e Silva; Davide Bianchi; David Brooks; Amanda Byström; Todd Claybaugh; Shaun Cole; Kyle Dawson; Axel de la Macorra; Jaime Forero-Romero; Oleg Y. Gnedin; Satya Gontcho A Gontcho; Gaston Gutierrez; Julien Guy; Klaus Honscheid; Robert Kehoe; Namitha Kizhuprakkat; Martin Landriau; Laurent Le Guillou; Michael Levi; Gustavo Medina Toledo; Aaron Meisner; Ramon Miquel; John Moustakas; Claire Poppett; Francisco Prada; Graziano Rossi; Eusebio Sánchez; Michael Schubnell; Ray Sharples; David Sprayberry; José Arturo Trelles Hernández; Benjamin Alan Weaver; Hu Zou

doi:10.1093/mnras/staf705

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

Bokyoung Kim^*, Sergey E. Koposov, Ting S. Li, Sophia Lilleengen, Andrew P. Cooper, Andreia Carrillo, Monica Valluri, Alexander H. Riley, Jiwon Jesse Han, Jessica Nicole Aguilar, Steven Ahlen, Leandro Beraldo e Silva, Davide Bianchi, David Brooks, Amanda Byström, Todd Claybaugh, Shaun Cole, Kyle Dawson, Axel de la Macorra, Jaime Forero-RomeroOleg Y. Gnedin, Satya Gontcho A Gontcho, Gaston Gutierrez, Julien Guy, Klaus Honscheid, Robert Kehoe, Namitha Kizhuprakkat, Martin Landriau, Laurent Le Guillou, Michael Levi, Gustavo Medina Toledo, Aaron Meisner, Ramon Miquel, John Moustakas, Claire Poppett, Francisco Prada, Graziano Rossi, Eusebio Sánchez, Michael Schubnell, Ray Sharples, David Sprayberry, José Arturo Trelles Hernández, Benjamin Alan Weaver, Hu Zou

^*Corresponding author for this work

School of Physics and Astronomy

Research output: Contribution to journal › Article › peer-review

Abstract

We report five nearby (d_helio < 5 kpc) stellar substructures in the Galactic halo from a subset of 138661 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_tot, L_z, log J_r, log J_z) space and Galactocentric cylindrical velocity space (V_R, V_φ, 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 characterised 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.

Original language	English
Pages (from-to)	264-288
Number of pages	25
Journal	Monthly Notices of the Royal Astronomical Society
Volume	540
Issue number	1
Early online date	1 May 2025
DOIs	https://doi.org/10.1093/mnras/staf705
Publication status	Published - 1 Jun 2025

Keywords / Materials (for Non-textual outputs)

surveys
Galaxy: halo
(Galaxy:) solar neighbourhood
Galaxy: kinematics and dynamics
stars: abundances

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10.1093/mnras/staf705Licence: Creative Commons: Attribution (CC-BY)

https://arxiv.org/abs/2504.20327Licence: Creative Commons: Attribution (CC-BY)

Probing dark matter distribution in the Milky Way with the DESI survey
Koposov, S. (Principal Investigator) & Penarrubia, J. (Co-investigator)
Science and Technology Facilities Council
1/04/24 → 31/03/28
Project: Research

Cite this

Kim, B., Koposov, S. E., Li, T. S., Lilleengen, S., Cooper, A. P., Carrillo, A., Valluri, M., Riley, A. H., Han, J. J., Aguilar, J. N., Ahlen, S., Silva, L. B. E., Bianchi, D., Brooks, D., Byström, A., Claybaugh, T., Cole, S., Dawson, K., Macorra, A. D. L., ... Zou, H. (2025). Nearby stellar substructures in the Galactic halo from DESI Milky Way Survey Year 1 Data Release. Monthly Notices of the Royal Astronomical Society , 540(1), 264-288. https://doi.org/10.1093/mnras/staf705

@article{83362f7866004cda985ee1005dd3436f,

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

abstract = "We report five nearby (dhelio < 5 kpc) stellar substructures in the Galactic halo from a subset of 138661 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 (Etot, Lz, log Jr, log Jz) space and Galactocentric cylindrical velocity space (VR, Vφ, Vz). 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 characterised 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.",

keywords = "surveys, Galaxy: halo, (Galaxy:) solar neighbourhood, Galaxy: kinematics and dynamics, stars: abundances",

author = "Bokyoung Kim and Koposov, {Sergey E.} and Li, {Ting S.} and Sophia Lilleengen and Cooper, {Andrew P.} and Andreia Carrillo and Monica Valluri and Riley, {Alexander H.} and Han, {Jiwon Jesse} and Aguilar, {Jessica Nicole} and Steven Ahlen and Silva, {Leandro Beraldo e} and Davide Bianchi and David Brooks and Amanda Bystr{\"o}m and Todd Claybaugh and Shaun Cole and Kyle Dawson and Macorra, {Axel de la} and Jaime Forero-Romero and Gnedin, {Oleg Y.} and Gontcho, {Satya Gontcho A} and Gaston Gutierrez and Julien Guy and Klaus Honscheid and Robert Kehoe and Namitha Kizhuprakkat and Martin Landriau and Guillou, {Laurent Le} and Michael Levi and Toledo, {Gustavo Medina} and Aaron Meisner and Ramon Miquel and John Moustakas and Claire Poppett and Francisco Prada and Graziano Rossi and Eusebio S{\'a}nchez and Michael Schubnell and Ray Sharples and David Sprayberry and Hern{\'a}ndez, {Jos{\'e} Arturo Trelles} and Weaver, {Benjamin Alan} and Hu Zou",

note = "25 pages, 12 figures, 6 tables. Accepted for publication in MNRAS",

year = "2025",

month = jun,

day = "1",

doi = "10.1093/mnras/staf705",

language = "English",

volume = "540",

pages = "264--288",

journal = "Monthly Notices of the Royal Astronomical Society ",

issn = "0035-8711",

publisher = "Oxford University Press",

number = "1",

}

Kim, B, Koposov, SE, Li, TS, Lilleengen, S, Cooper, AP, Carrillo, A, Valluri, M, Riley, AH, Han, JJ, Aguilar, JN, Ahlen, S, Silva, LBE, Bianchi, D, Brooks, D, Byström, A, Claybaugh, T, Cole, S, Dawson, K, Macorra, ADL, Forero-Romero, J, Gnedin, OY, Gontcho, SGA, Gutierrez, G, Guy, J, Honscheid, K, Kehoe, R, Kizhuprakkat, N, Landriau, M, Guillou, LL, Levi, M, Toledo, GM, Meisner, A, Miquel, R, Moustakas, J, Poppett, C, Prada, F, Rossi, G, Sánchez, E, Schubnell, M, Sharples, R, Sprayberry, D, Hernández, JAT, Weaver, BA & Zou, H 2025, 'Nearby stellar substructures in the Galactic halo from DESI Milky Way Survey Year 1 Data Release', Monthly Notices of the Royal Astronomical Society , vol. 540, no. 1, pp. 264-288. https://doi.org/10.1093/mnras/staf705

TY - JOUR

T1 - Nearby stellar substructures in the Galactic halo from DESI Milky Way Survey Year 1 Data Release

AU - Kim, Bokyoung

AU - Koposov, Sergey E.

AU - Li, Ting S.

AU - Lilleengen, Sophia

AU - Cooper, Andrew P.

AU - Carrillo, Andreia

AU - Valluri, Monica

AU - Riley, Alexander H.

AU - Han, Jiwon Jesse

AU - Aguilar, Jessica Nicole

AU - Ahlen, Steven

AU - Silva, Leandro Beraldo e

AU - Bianchi, Davide

AU - Brooks, David

AU - Byström, Amanda

AU - Claybaugh, Todd

AU - Cole, Shaun

AU - Dawson, Kyle

AU - Macorra, Axel de la

AU - Forero-Romero, Jaime

AU - Gnedin, Oleg Y.

AU - Gontcho, Satya Gontcho A

AU - Gutierrez, Gaston

AU - Guy, Julien

AU - Honscheid, Klaus

AU - Kehoe, Robert

AU - Kizhuprakkat, Namitha

AU - Landriau, Martin

AU - Guillou, Laurent Le

AU - Levi, Michael

AU - Toledo, Gustavo Medina

AU - Meisner, Aaron

AU - Miquel, Ramon

AU - Moustakas, John

AU - Poppett, Claire

AU - Prada, Francisco

AU - Rossi, Graziano

AU - Sánchez, Eusebio

AU - Schubnell, Michael

AU - Sharples, Ray

AU - Sprayberry, David

AU - Hernández, José Arturo Trelles

AU - Weaver, Benjamin Alan

AU - Zou, Hu

N1 - 25 pages, 12 figures, 6 tables. Accepted for publication in MNRAS

PY - 2025/6/1

Y1 - 2025/6/1

N2 - We report five nearby (dhelio < 5 kpc) stellar substructures in the Galactic halo from a subset of 138661 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 (Etot, Lz, log Jr, log Jz) space and Galactocentric cylindrical velocity space (VR, Vφ, Vz). 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 characterised 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.

AB - We report five nearby (dhelio < 5 kpc) stellar substructures in the Galactic halo from a subset of 138661 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 (Etot, Lz, log Jr, log Jz) space and Galactocentric cylindrical velocity space (VR, Vφ, Vz). 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 characterised 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.

KW - surveys

KW - Galaxy: halo

KW - (Galaxy:) solar neighbourhood

KW - Galaxy: kinematics and dynamics

KW - stars: abundances

U2 - 10.1093/mnras/staf705

DO - 10.1093/mnras/staf705

M3 - Article

SN - 0035-8711

VL - 540

SP - 264

EP - 288

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

IS - 1

ER -

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

Abstract

Keywords / Materials (for Non-textual outputs)

Access to Document

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Projects

Probing dark matter distribution in the Milky Way with the DESI survey

Cite this