Mapping the Milky Way with LAMOST– III. Complicated spatial structure in the outer disc

By Haifeng Wang, Chao Liu, Yan Xu, Jun-Chen Wan, Licai Deng. 2018

56 citations recorded by the source corpus.

We present {complexity} of the Galactic outer disc {by fitting the stellar volume densities of the red giant branch stars with a two-disc component model}. {The discs are confirmed to} extend to $R\sim19$\,kpc. The radial density profile of the discs shows {two breaks at $R\sim11$ and $\sim14$\,kpc, respectively, which} separate the radial profile into three segments with different scale lengths of $2.12\pm0.26$, $1.18\pm0.08$, and $2.72$\,kpc at $R 14$\,kpc, respectively. The first {break} is likely due to the sudden drop in the radial profile of the thin disc, which may be an evidence of the radial migration. {Beyond $14$\,kpc, the thick disc becomes prominent and the transition from thin to thick disc leads to the second break.} This implies that the geometrically defined thick disc is more {radially} extended than the thin disc. This is also supported by the larger scale length of the thick disc than that of the thin disc. Meanwhile, {the scale height of the thicker component increases from $0.637_{-0.036}^{+0.056}$ at $R=8$ to $1.284_{-0.079}^{+0.086}$\,kpc at $R=19$\,kpc, showing an intensive flared disc}. Moreover, rich substructures are displayed in the residuals of the stellar density. Among them, the substructures $D14+2.0$ and $O14-1.5$ show a north-south asymmetry, which can be essentially explained by southward shifting of the thick disc. However, no significant overdensity is found for the Monoceros ring. Finally, the thick disc shows a ripple-like feature with unclear origin at $9

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Citations in the corpus

Yule-Simpson’s paradox in Galactic Archaeology (2019, background): “…Way stellar populations of limited age range has been found by Kalberla et al. (2014) (Red Clump), Feast et al. (2014) (Cepheids), Carraro et al. (2015) (young clusters) and in LAMOST (Wan et al. 2017; Wang et al. 2018; Xiang et al. 2018) and APOGEE (Mackereth et al. 2017) mono-age populations.”
Painting a portrait of the Galactic disc with its stellar clusters (2020, background): “…Kalberla et al. (2007) and Kalberla & Dedes (2008), who could trace atomic hydrogen out to much larger distances than our cluster sample, show that the flaring of HI gas outside the Solar circle is better reproduced with an exponential function, and Wang et al. (2018) used a quadratic function.”