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

Abstract

We explore the contribution of the Gaia-Sausage to the stellar halo of the Milky Way by making use of a Gaussian Mixture model (GMM) and applying it to halo star samples of LAMOST K giants, SEGUE K giants, and SDSS blue horizontal branch stars. The GMM divides the stellar halo into two parts, of which one represents a more metal-rich and highly radially biased component associated with an ancient, head-on collision referred to as the Gaia-Sausage, and the other one is a more metal-poor and isotropic halo. A symmetric bimodal Gaussian is used to describe the distribution of spherical velocity of the Gaia-Sausage, and we find that the mean absolute radial velocity of the two lobes decreases with Galactocentric radius. We find that the Gaia-Sausage contributes about $41\%-74\%$ of the inner (Galactocentric radius $r_{\mathrm{gc}}<30$ kpc) stellar halo. The fraction of stars of the Gaia-Sausage starts to decline beyond $r_{\mathrm{gc}}\sim$ $25-30$ kpc, and the outer halo is found to be significantly less influenced by the Gaia-Sausage than the inner halo. After the removal of halo substructures found by integrals of motion, the contribution of the \textit{Gaia}-Sausage falls slightly within $r_{\mathrm{gc}}\sim$ 25 kpc, but is still as high as $30\%-63\%$. Finally, we select several possible Sausage-related substructures consisting of stars on highly eccentric orbits. The GMM/Sausage component agrees well with the selected substructure stars in their chemodynamical properties, which increases our confidence in the reliability of the GMM fits.

accepted for publication in ApJ

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• Milky Way Mass with K Giants and BHB Stars Using LAMOST, SDSS/SEGUE, and Gaia: 3D Spherical Jeans Equation and Tracer Mass Estimator
• Mapping the anisotropic Galactic stellar halo with Blue Horizontal Branch stars
• Probing the Galactic halo with RR Lyrae stars $-$ III. The chemical and kinematic properties of the stellar halo
• Four-hundred Very Metal-poor Stars Studied with LAMOST and Subaru. III. Dynamically Tagged Groups and Chemodynamical Properties
• Constructing the Milky Way Stellar Halo in the Galactic Center by Direct Orbit Integration
• The SDSS-Gaia View of the Color-Magnitude Relation for Blue Horizontal-branch Stars
• Influence of the Gaia-Sausage-Enceladus on the density shape of the Galactic stellar halo revealed by halo K giants from the LAMOST survey
• Exploring the ex-situ components within Gaia DR3
• HALO7D III: Chemical Abundances of Milky Way Halo Stars from Medium Resolution Spectra
• Probing the Galactic halo with RR Lyrae stars -- IV. On the Oosterhoff dichotomy of RR Lyrae stars
• Deciphering the Kinematic Substructure of Local Dark Matter with LAMOST K Giants