Mapping the Milky Way with LAMOST I: Method and overview

Abstract

We present a statistical method to derive the stellar density profiles of the Milky Way from spectroscopic survey data, taking into account selection effects. We assume that the selection function of the spectroscopic survey is based on photometric colors and magnitudes and possibly altered during observations and data reductions. Then the underlying selection function for a line-of-sight can be well recovered by comparing the distribution of the spectroscopic stars in a color-magnitude plane with that of the photometric dataset. Subsequently, the stellar density profile along a line-of-sight can be derived from the spectroscopically measured stellar density profile multiplied by the selection function. The method is validated using Galaxia mock data with two different selection functions. We demonstrate that the derived stellar density profiles well reconstruct the true ones not only for the full targets, but also for the sub-populations selected from the full dataset. Finally, the method is applied to map the density profiles for the Galactic disk and halo, respectively, using the LAMOST RGB stars. The Galactic disk extends to about R=19 kpc, where the disk still contributes about 10% to the total stellar surface density. Beyond this radius, the disk smoothly transitions to the halo without any truncation, bending, or broken. Moreover, no over-density corresponding to the Monoceros ring is found in the Galactic anti-center direction. The disk shows moderate north-south asymmetry at radii larger than 12 kpc. On the other hand, the R-Z tomographic map directly shows that the stellar halo is substantially oblate within a Galactocentric radius of 20 kpc and gradually becomes nearly spherical beyond 30 kpc.

27 pages, 18 figures, accepted by Research in Astronomy and Astrophysics

References in corpus (10)

• The Galaxy in Context: Structural, Kinematic and Integrated Properties
• The Milky Way Tomography with SDSS: II. Stellar Metallicity
• Rings and Radial Waves in the Disk of the Milky Way
• LAMOST Spectroscopic Survey of the Galactic Anti-centre (LSS-GAC): target selection and the first release of value-added catalogues
• The K giant stars from the LAMOST survey data I: identification, metallicity, and distance
• Cepheid Variables in the Flared Outer Disk of our Galaxy
• The Edge of the Milky Way Stellar Disk Revealed Using Clump Giant Stars as Distance Indicators
• Estimation of distances to stars with stellar parameters from LAMOST
• The asymmetric structure of the Galactic halo
• The structure of the Galactic halo: SDSS versus SuperCOSMOS

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• The Sample of Red Supergiants in Twelve Low-Mass Galaxies of the Local Group
• Chemical and kinematic analysis of CN-strong Metal-poor Field Stars in LAMOST DR3
• Identifying Galactic Halo Substructure in 6D Phase-space Using $\sim$13,000 LAMOST K Giants
• Structure of the outer Galactic disc with Gaia-DR2
• Effects of the selection function on metallicity trends in spectroscopic surveys of the Milky Way
• The Binarity of Early-type Stars from LAMOST Medium-resolution Spectroscopic Survey
• The Flare and Warp of the Young Stellar Disk traced with LAMOST DR5 OB-type stars
• 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
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• Red Clump stars from LAMOST II: the outer disc of the Milky Way
• Constructing the Milky Way Stellar Halo in the Galactic Center by Direct Orbit Integration
• An analysis of the most distant catalogued open clusters -- Re-assessing fundamental parameters with Gaia EDR3 and $\text{ASteCA}$
• Prospects for Detecting Gaps in Globular Cluster Stellar Streams in External Galaxies with the Nancy Grace Roman Space Telescope
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• The Density Profile and Kinematics of the Milky Way with RR Lyrae Stars
• Atmospheric parameters and kinematic information for the M giants stars from LAMOST DR9
• Rediscovering the Galactic outer disk with LAMOST data
• A Vertically Orientated Dark Matter Halo Marks a Flip of the Galactic Disk
• Detailed Mapping of the Galactic Disk Structure in the Solar Neighborhood through LAMOST K Dwarfs
• Stellar initial mass function in the 100-pc solar neighbourhood
• Uncover 3D Dark Matter Distribution of the Milky Way by an Empirical Triaxial Orbit-Superposition Model: Method Validation
• Mapping the Milky Way with Gaia Bp/Rp spectra-IV: the broken and asymmetric density profile of the stellar disk traced by a large sample of red clumps