Deciphering the Kinematic Substructure of Local Dark Matter with LAMOST K Giants

Abstract

Numerical simulations indicate that correlations exist between the velocity distributions of stars and dark matter (DM). We study the local DM velocity distribution based on these correlations. We select K giants from LAMOST DR8 cross-matched with {\gaia} DR3, which have robust measurements of velocity and metallicity, and separate them into the disk, halo substructure and isotropic halo components in the chemodynamical space utilizing the Gaussian Mixture Model. The substructure component is highly radially anisotropic, and possibly related to the \gaia-Enceladus-Sausage (GES) merger event, while the isotropic halo component is accreted from the earliest mergers following the Maxwell-Boltzmann distribution (Standard Halo Model, SHM). We find that the GES-like substructure contributes $\sim 85\%$ of the local nondisk stars in the Solar neighbourhood, which is nearly invariant when applying different volume cuts or additional angular momentum constraints. Utilizing the metallicity-stellar mass relation and the stellar mass-halo mass relation, we find that $\sim 25_{-15}^{+24}\%$ of local DM is in the kinematic substructure. Combined with the stellar distributions of nondisk components, we modify the heliocentric velocity distribution of local DM. It shifts to a lower speed with a sharper peak compared to the SHM, and updates the detection limits of DM direct detection experiments. We discuss extensively the degeneracies present in the GMM fitting and propose that more kinematic and chemical information such as $\alpha$ abundance could help to break the degeneracy in the future. Our work confirms that the local DM velocity distribution deviates significantly from the SHM, and needs to be properly accounted for in the DM detection experiments.

Published in ApJ, 27 pages, 17 figures, comments welcome

References in corpus (23)

• Gaia Data Release 3: Summary of the content and survey properties
• Dark Matter Search Results from the PandaX-4T Commissioning Run
• Evidence from the H3 Survey that the Stellar Halo is Entirely Comprised of Substructure
• From dawn till disk: Milky Way's turbulent youth revealed by the APOGEE+Gaia data
• The total stellar halo mass of the Milky Way
• The Fall of a Giant. Chemical evolution of Enceladus, alias the Gaia Sausage
• Timing the Early Assembly of the Milky Way with the H3 Survey
• $S^5$: Probing the Milky Way and Magellanic Clouds potentials with the 6-D map of the Orphan-Chenab stream
• The GALAH Survey: Chemical tagging and chrono-chemodynamics of accreted halo stars with GALAH+ DR3 and $Gaia$ eDR3
• The K giant stars from the LAMOST survey data I: identification, metallicity, and distance
• The Circular Velocity Curve of the Milky Way from 5 to 25 kpc using luminous red giant branch star
• Measuring the local dark matter density with LAMOST DR5 and Gaia DR2
• Energy wrinkles and phase-space folds of the last major merger
• A skewer survey of the Galactic halo from deep CFHT and INT images
• Tracing Kinematic and Chemical Properties of Sagittarius Stream by K-Giants, M-Giants, and BHB stars
• The Local Stellar Halo is Not Dominated by a Single Radial Merger Event
• The impact of the Large Magellanic Cloud on dark matter direct detection signals
• A Swing of the Pendulum: The Chemodynamics of the Local Stellar Halo Indicate Contributions from Several Radial Merger Events
• Contribution of Gaia Sausage to the Galactic Stellar Halo Revealed by K Giants and Blue Horizontal Branch Stars from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, Sloan Digital Sky Survey, and Gaia
• Effects on the local dark matter distribution due to the Large Magellanic Cloud
• Dark matter substructures affect dark matter-electron scattering in xenon-based direct detection experiments
• The North/South Asymmetry of the Galaxy: Possible Connection to the Vertical Phase Space Snail
• Vertical structure of Galactic disk kinematics from LAMOST K giants

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• Dark Matter Velocity Distributions for Direct Detection: Astrophysical Uncertainties are Smaller Than They Appear
• The Pristine Survey -- XXVII. Journey to the Galactic outskirts -- Mapping the outer halo red giant stars down to the very metal-poor end
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