East Asian VLBI Network astrometry toward the star-forming region G040.96+02.48 in the Extreme Outer Galaxy

Xianjin Shen; Zehao Lin; Nobuyuki Sakai; Ye Xu; Shuaibo Bian; Yuanwei Wu; Yan Sun; Dejian Liu; Jingjing Li; Bo Zhang; Shuangjing Xu; Tomoaki Oyama; Chungsik Oh; Wu Jiang; Lang Cui; Pengfei Jiang; Guanghui Li; Mareki Honma; Se-Jin Oh; Zhi-Qiang Shen; Na Wang

arXiv · 2604.23963

East Asian VLBI Network astrometry toward the star-forming region G040.96+02.48 in the Extreme Outer Galaxy

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Abstract

Accurate astrometric measurements for star-forming regions located on the far side of the Milky Way remain scarce. In this work, we present the astrometric results for a 22\,GHz water maser associated with star-forming region G040.96+02.48 located on the far side of the Milky Way, using the East Asian VLBI Network. The target water maser's proper motion was determined to be ($μ_α\cosδ, μ_δ$) = ($-2.06_{-0.51}^{+0.53}$, $-2.95_{-0.44}^{+0.45}$)~mas~yr$^{-1}$. The derived three-dimensional kinematic distance to the star-forming region is 20.2$\pm$3.2\,kpc, placing it slightly outside the Outer Scutum$-$Centaurus Arm. The corresponding vertical height of 872$\pm$139\,pc indicates a significant warp of the outer Galactic disk, which is in good agreement with the latest precessing warp model. Moreover, the resulting peculiar motions reveal a complex kinematic pattern, characterized by a large outward radial velocity of $-32\pm$18\,km~s$^{-1}$. Our observations substantially expand the valuable sample of star-forming regions with accurate astrometric measurements in the Extreme Outer Galaxy.

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Xianjin Shen, Zehao Lin, Nobuyuki Sakai, Ye Xu, Shuaibo Bian, Yuanwei Wu, Yan Sun, Dejian Liu, Jingjing Li, Bo Zhang, Shuangjing Xu, Tomoaki Oyama, Chungsik Oh, Wu Jiang, Lang Cui, Pengfei Jiang, Guanghui Li, Mareki Honma, Se-Jin Oh, Zhi-Qiang Shen, Na Wang. 2026-04-27. East Asian VLBI Network astrometry toward the star-forming region G040.96+02.48 in the Extreme Outer Galaxy. https://arxiv.org/abs/2604.23963

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