Differential rotation of the halo traced by the K-giant stars

Abstract

We use K-giant stars selected from the LAMOST DR5 to study the variation of the rotational velocity of the galactic halo at different space positions. Modelling the rotational velocity distribution with both the halo and disk components, we find that the rotational velocity of the halo population decreases almost linearly with increasing vertical distance to the galactic disk plane, $Z$, at fixed galactocentric radius, $R$. The samples are separated into two parts with $6<R<12$ kpc and $12<R<20$ kpc. We derive that the decreasing rates along $Z$ for the two subsamples are $-3.07\pm 0.63$ and $-1.89\pm 0.37$ km s${}^{-1}$ kpc${}^{-1}$, respectively. Compared with the TNG simulations, we suggest that this trend is probably caused by the interaction between the disk and halo. The results from the simulations show that only the oblate halo can provide a decreasing rotational velocity with an increasing $Z$. This indicates that the Galactic halo is oblate with galactocentric radius $R<20$ kpc. On the other hand, the flaring of the disk component (mainly the thick disk) is clearly traced by this study, with $R$ between 12 and 20 kpc, the disk can vertically extend to $6\sim 10$ kpc above the disk plane. What is more interesting is that, we find the Gaia-Enceladus-Sausage (GES) component has a significant contribution only in the halo with $R<12$ kpc, i.e. a fraction of 23$-$47\%. While in the outer subsample, the contribution is too low to be well constrained.

arXiv commentAccepted for publication in ApJ, 18 pages, 12 figures, 1 table

References in corpus (63)

• Astropy: A Community Python Package for Astronomy
• emcee: The MCMC Hammer
• The Sloan Digital Sky Survey: Technical Summary
• Gaia Data Release 2. Summary of the contents and survey properties
• The Gaia mission
• Simulating Galaxy Formation with the IllustrisTNG Model
• Local Kinematics and the Local Standard of Rest
• First results from the IllustrisTNG simulations: matter and galaxy clustering
• The Apache Point Observatory Galactic Evolution Experiment (APOGEE)
• Estimating distances from parallaxes IV: Distances to 1.33 billion stars in Gaia Data Release 2
• First results from the IllustrisTNG simulations: the stellar mass content of groups and clusters of galaxies
• The Galaxy in Context: Structural, Kinematic and Integrated Properties
• First results from the IllustrisTNG simulations: the galaxy color bimodality
• galpy: A Python Library for Galactic Dynamics
• Trigonometric Parallaxes of High Mass Star Forming Regions: the Structure and Kinematics of the Milky Way
• First results from the IllustrisTNG simulations: A tale of two elements -- chemical evolution of magnesium and europium
• Simulating galaxy formation with black hole driven thermal and kinetic feedback
• The merger that led to the formation of the Milky Way's inner stellar halo and thick disk
• SEGUE: A Spectroscopic Survey of 240,000 stars with g=14-20
• First results from the IllustrisTNG simulations: radio haloes and magnetic fields
• Substructures in hydrodynamical cluster simulations
• Co-formation of the Galactic disc and the stellar halo
• A model for cosmological simulations of galaxy formation physics
• The Milky Way's Circular Velocity Curve to 60 kpc and an Estimate of the Dark Matter Halo Mass from Kinematics of ~2400 SDSS Blue Horizontal Branch Stars
• Two Stellar Components in the Halo of the Milky Way
• Chemical Cartography with APOGEE: Metallicity Distribution Functions and the Chemical Structure of the Milky Way Disk
• The Sagittarius Dwarf Galaxy: a Model for Evolution in a Triaxial Milky Way Halo
• Evidence for Two Early Accretion Events That Built the Milky Way Stellar Halo
• A dynamically young and perturbed Milky Way disk
• Gaia Data Release 2: Mapping the Milky Way disc kinematics
• Dynamical modelling of the Galactic bulge and bar: the Milky Way's bar pattern speed, stellar, and dark matter mass distribution
• Detection of a 63 Degree Cold Stellar Stream in the Sloan Digital Sky Survey
• A physical model for cosmological simulations of galaxy formation: multi-epoch validation
• The Biggest Splash
• Footprints of the Sagittarius dwarf galaxy in the $Gaia$ data set
• Rings and Radial Waves in the Disk of the Milky Way
• The role of mergers and halo spin in shaping galaxy morphology
• Constraints on the shape of the Milky Way dark matter halo from the Sagittarius stream
• A 22 Degree Tidal Tail for Palomar 5
• The Stellar Metallicity Distribution Function of the Galactic Halo from SDSS Photometry
• A Synoptic Map of Halo Substructures from the Pan-STARRS1 3π Survey
• The K giant stars from the LAMOST survey data I: identification, metallicity, and distance
• Mapping the Milky Way with LAMOST III: Complicated spatial structure in the outer disc
• Galactic Archeology with the AEGIS Survey: The Evolution of Carbon and Iron in the Galactic Halo
• Predicted Extension of the Sagittarius Stream to the Milky Way Virial Radius
• Action-space clustering of tidal streams to infer the Galactic potential
• Anisotropy of the Milky Way's stellar halo using K giants from LAMOST and $Gaia$
• A New Model for the Milky Way Bar
• The Profile of the Galactic Halo from Pan-STARRS1 3$\pi$ RR Lyrae
• Chemo-orbital evidence from SDSS/SEGUE G-type dwarf stars for a mixed origin of the Milky Way's thick disk
• Assessing distances and consistency of kinematics in Gaia/TGAS
• Probing the shape and history of the Milky Way halo with orbital spectral analysis
• Evidence for the Third Stellar Population in the Milky Way's Disk
• A-type stars in the Canada-France Imaging Survey I. The stellar halo of the Milky Way traced to large radius by blue horizontal branch stars
• On Rings and Streams in the Galactic Anti-Center
• Made-to-measure galaxy models - III Modelling with Milky Way observations
• Constraining the Milky Way Halo Shape Using Thin Streams
• Deep SDSS optical spectroscopy of distant halo stars II. Iron, calcium, and magnesium abundances
• Estimation of distances to stars with stellar parameters from LAMOST
• Mapping the Milky Way with LAMOST II: the stellar halo
• Rotating halo traced by the K giant stars from LAMOST and Gaia
• A Schwarzschild model of the Galactic bar with initial density from N-body simulations
• Orbit properties of massive prolate galaxies in the Illustris simulation

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• Self-consistent Stellar Radial Velocities from LAMOST Medium-Resolution Survey (MRS) DR7
• Overview of the LAMOST survey in the first decade
• Exploring the origin of low-metallicity stars in Milky Way-like galaxies with the NIHAO-UHD simulations
• Constraints on the assembly history of the Milky Way's smooth, diffuse stellar halo from the metallicity-dependent, radially-dominated velocity anisotropy profiles probed with K giants and BHB stars using LAMOST, SDSS/SEGUE, and Gaia
• A three-dimensional map of the Milky Way using 66,000 Mira variable stars
• Constructing the Milky Way Stellar Halo in the Galactic Center by Direct Orbit Integration
• Atmospheric parameters and kinematic information for the M giants stars from LAMOST DR9
• Search for the metal-weak thick disk from the LAMOST DR5
• The Relative Calibration of Radial Velocity for LAMOST Medium Resolution Stellar Spectra