Search for the metal-weak thick disk from the LAMOST DR5
T.-S. Yan, J.-R. Shi, H. Tian, W. Zhang, B. Zhang

TL;DR
This study uses LAMOST DR5 and Gaia EDR3 data to identify and analyze the metal-weak thick disk component in the Milky Way, providing evidence for inside-out disk formation.
Contribution
It presents the first large-scale observational evidence of the metal-weak thick disk's properties and its spatial variation, supporting inside-out galaxy formation models.
Findings
MWTD is significant in the inner region at high [$ mf extalpha$/Fe] and low [Fe/H]
MWTD appears only at very low [Fe/H] in the outer region
Inner region has a higher fraction of MWTD than outer region
Abstract
Based on the data release of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope survey (LAMOST DR5) and the \emph{Gaia} Early Data Release 3 (\emph{Gaia} EDR3), we construct a sample containing 46,109 giant (log~ 3.5\,dex) stars with heliocentric distance d 4 kpc, and the sample is further divided into two groups of the inner ({\RGC} 8.34 \,kpc) and outer region ({\RGC} 8.34\,kpc). The {\LZ} distributions of our program stars in the panels with different [Fe/H] and [/Fe] suggest that the thick-disk consists of two distinct components with different chemical compositions and kinematic properties. For the inner region, the metal-weak thick disk (MWTD) contributes significantly when [/Fe] 0.2\,dex and [Fe/H] 0.8\,dex, while the canonical thick-disk (TD) dominates when [Fe/H]0.8\,dex. However, MWTD clearly…
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