East Asian VLBI Network Astrometry Toward the Star-forming Region G040.96+02.48 in the Extreme Outer Galaxy

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 Very Long Baseline Interferometry Network. The target water maser’s proper motion was determined to be ( μ α cos δ , μ δ ) = ( − 2.0 6 − 0.51 + 0.53 , − 2.9 5 − 0.44 + 0.45 ) mas yr −1 . The derived three-dimensional kinematic distance to the star-forming region is 20.2 ± 3.2 kpc, placing it slightly outside the Outer Scutum−Centaurus Arm. The corresponding vertical height of 872 ± 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 ± 18 km s −1 . Our observations substantially expand the valuable sample of star-forming regions with accurate astrometric measurements in the Extreme Outer Galaxy.