Detailed Mapping of the Galactic Disk Structure in the Solar Neighborhood through LAMOST K Dwarfs

TL;DR

This study uses a large sample of K dwarf stars from LAMOST and Gaia to map the detailed structure of the Milky Way's Galactic disk, revealing significant asymmetries and variations in scale height related to azimuth, vertical position, and metallicity.

Contribution

It provides the first detailed 3D mapping of the local Galactic disk structure highlighting non-axisymmetric features and metallicity-dependent vertical variations.

Findings

Detected strong azimuthal asymmetry in the thin disk.

Found different vertical scale height trends in northern and southern disks.

Observed metallicity-dependent variations in disk scale height.

Abstract

The Galactic disk is one of the main components of the Milky Way, which contributes most of the luminosity. Its structure is essential for understanding the formation and evolution of the Milky Way. Using 174,443 K-type dwarf stars observed by both LAMOST and Gaia DR3, we study the disk density profile in the local volume within 1,200 pc. In the azimuthal dimension, we find strong asymmetric signal of the thin disk. The surface density and the scale height of the southern disk significantly change versus the azimuthal angle at the same galactocentric distance $R$. Meanwhile, in the vertical dimension, the scale height of the northern disk has quite different trend than that of the southern one. The scale height of the southern disk shows a decreasing trend with $\phi\sim-2.5^\circ$, and change to an increasing one with $\phi\sim5.0^\deg$. Meanwhile, the scale height of the northern disk has a consistently smaller increase. Finally, we divide the entire sample into three subsamples based on metallicity and all three subsamples show significant non-axisymmetric and north-south asymmetric signals in the Galactic disk. Furthermore, we find that the scale height of the metal-poor ([Fe/H] $<$ -0.4 dex) subsample in the northern disk is greater than that of the metal-rich ([Fe/H] $>$ -0.1 dex) subsample. However, in the southern disk, the scale height exhibits varying relationships across different metallicity slices.