The velocity field of our Milky Way outer stellar halo based on DESI DR2
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2026
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| author | Li, Songting Wang, Wenting Koposov, Sergey E. Amarante, João A. S. Deason, Alis J. Valluri, Monica Li, Ting S. Byström, Amanda Lambert, Mika Qiu, Tian Najita, Joan Medina, Gustavo E. Gnedin, Oleg Y. Silva, Leandro Beraldo e Brooks, Richard A. N. Carlberg, Raymond G. Kizhuprakkat, Namitha Han, Jiaxin Aguilar, Jessica Nicole Ahlen, Steven Bianchi, Davide Brooks, David Claybaugh, Todd Cuceu, Andrei de la Macorra, Axel Doel, Peter Font-Ribera, Andreu Forero-Romero, Jaime E. Ferraro, Simone Gaztañaga, Enrique Gontcho, Satya Gontcho A Gutierrez, Gaston Guy, Julien Honscheid, Klaus Joyce, Dick Kremin, Anthony Landriau, Martin Guillou, Laurent Le Meisner, Aaron Miquel, Ramon Moustakas, John Nadathur, Seshadri Percival, Will Prada, Francisco Pérez-Ràfols, Ignasi Rossi, Graziano Sanchez, Eusebio Schlegel, David Schubnell, Michael Sharples, Ray Silber, Joseph Harry Sprayberry, David Tarlé, Gregory Weaver, Benjamin Alan Zhou, Rongpu Zou, Hu |
| author_facet | Li, Songting Wang, Wenting Koposov, Sergey E. Amarante, João A. S. Deason, Alis J. Valluri, Monica Li, Ting S. Byström, Amanda Lambert, Mika Qiu, Tian Najita, Joan Medina, Gustavo E. Gnedin, Oleg Y. Silva, Leandro Beraldo e Brooks, Richard A. N. Carlberg, Raymond G. Kizhuprakkat, Namitha Han, Jiaxin Aguilar, Jessica Nicole Ahlen, Steven Bianchi, Davide Brooks, David Claybaugh, Todd Cuceu, Andrei de la Macorra, Axel Doel, Peter Font-Ribera, Andreu Forero-Romero, Jaime E. Ferraro, Simone Gaztañaga, Enrique Gontcho, Satya Gontcho A Gutierrez, Gaston Guy, Julien Honscheid, Klaus Joyce, Dick Kremin, Anthony Landriau, Martin Guillou, Laurent Le Meisner, Aaron Miquel, Ramon Moustakas, John Nadathur, Seshadri Percival, Will Prada, Francisco Pérez-Ràfols, Ignasi Rossi, Graziano Sanchez, Eusebio Schlegel, David Schubnell, Michael Sharples, Ray Silber, Joseph Harry Sprayberry, David Tarlé, Gregory Weaver, Benjamin Alan Zhou, Rongpu Zou, Hu |
| contents | Using 64,000 halo K giants from Dark Energy Spectroscopic Instrument (DESI) second Data Release (DR2), we decompose the Milky Way (MW) stellar halo between 3 and 160 kpc into metal-rich (MR) and metal-poor (MP) components via a Gaussian mixture model (GMM). The two populations are nearly equal in number but chemically and kinematically distinct: MR stars occupy highly radial orbits with velocity anisotropy of beta ~0.94 and metallicity dispersion sigma([Fe/H]) ~0.17 dex, without obvious dependence on distance, and are mainly contributed by Gaia-Sausage/Enceladus (GSE) debris. MR component dominates the inner 30 kpc and re-emerges beyond 50 kpc, implying GSE debris can extend to ~70-80 kpc. MP stars exhibit a weaker radial bias of beta ~0.46, decreasing to -0.5 beyond 80 kpc, and with a larger metallicity dispersion of sigma([Fe/H]) ~0.46 dex, showing signatures of multiple minor mergers. Both components exhibit net prograde rotation at ~10-30 kpc with a stronger azimuthal signal in the MP population. The non-equilibrium motions of the outer halo (>50 kpc) are quantified with a dipole-plus-contraction velocity field. We find that the outer halo is simultaneously contracting (~-19 km/s, distance-independent) and subject to reflex motions (increases from -19 to -44 km/s with radius), reflecting the perturbation from the Large Magellanic Cloud (LMC). We also confirm a linear dependence of mean polar velocity for the outer stellar halo on the dipole velocity field, a direct consequence of the LMC and MW interaction. Our results provide a quantitative distance-resolved description of the MW's last major accretion event and its ongoing response to the first infall of the LMC. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2604_01628 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | The velocity field of our Milky Way outer stellar halo based on DESI DR2 Li, Songting Wang, Wenting Koposov, Sergey E. Amarante, João A. S. Deason, Alis J. Valluri, Monica Li, Ting S. Byström, Amanda Lambert, Mika Qiu, Tian Najita, Joan Medina, Gustavo E. Gnedin, Oleg Y. Silva, Leandro Beraldo e Brooks, Richard A. N. Carlberg, Raymond G. Kizhuprakkat, Namitha Han, Jiaxin Aguilar, Jessica Nicole Ahlen, Steven Bianchi, Davide Brooks, David Claybaugh, Todd Cuceu, Andrei de la Macorra, Axel Doel, Peter Font-Ribera, Andreu Forero-Romero, Jaime E. Ferraro, Simone Gaztañaga, Enrique Gontcho, Satya Gontcho A Gutierrez, Gaston Guy, Julien Honscheid, Klaus Joyce, Dick Kremin, Anthony Landriau, Martin Guillou, Laurent Le Meisner, Aaron Miquel, Ramon Moustakas, John Nadathur, Seshadri Percival, Will Prada, Francisco Pérez-Ràfols, Ignasi Rossi, Graziano Sanchez, Eusebio Schlegel, David Schubnell, Michael Sharples, Ray Silber, Joseph Harry Sprayberry, David Tarlé, Gregory Weaver, Benjamin Alan Zhou, Rongpu Zou, Hu Astrophysics of Galaxies Solar and Stellar Astrophysics Using 64,000 halo K giants from Dark Energy Spectroscopic Instrument (DESI) second Data Release (DR2), we decompose the Milky Way (MW) stellar halo between 3 and 160 kpc into metal-rich (MR) and metal-poor (MP) components via a Gaussian mixture model (GMM). The two populations are nearly equal in number but chemically and kinematically distinct: MR stars occupy highly radial orbits with velocity anisotropy of beta ~0.94 and metallicity dispersion sigma([Fe/H]) ~0.17 dex, without obvious dependence on distance, and are mainly contributed by Gaia-Sausage/Enceladus (GSE) debris. MR component dominates the inner 30 kpc and re-emerges beyond 50 kpc, implying GSE debris can extend to ~70-80 kpc. MP stars exhibit a weaker radial bias of beta ~0.46, decreasing to -0.5 beyond 80 kpc, and with a larger metallicity dispersion of sigma([Fe/H]) ~0.46 dex, showing signatures of multiple minor mergers. Both components exhibit net prograde rotation at ~10-30 kpc with a stronger azimuthal signal in the MP population. The non-equilibrium motions of the outer halo (>50 kpc) are quantified with a dipole-plus-contraction velocity field. We find that the outer halo is simultaneously contracting (~-19 km/s, distance-independent) and subject to reflex motions (increases from -19 to -44 km/s with radius), reflecting the perturbation from the Large Magellanic Cloud (LMC). We also confirm a linear dependence of mean polar velocity for the outer stellar halo on the dipole velocity field, a direct consequence of the LMC and MW interaction. Our results provide a quantitative distance-resolved description of the MW's last major accretion event and its ongoing response to the first infall of the LMC. |
| title | The velocity field of our Milky Way outer stellar halo based on DESI DR2 |
| topic | Astrophysics of Galaxies Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2604.01628 |