2D projections in Galactocentric Cartesian coordinates, with the Sun at (X, Y, Z) = (0 kpc, 8.15 kpc, 0 kpc) (orange circle with dot). The Galactic center is marked as an orange plus. The gray circles denote the SiO masers found in the survey, whose arrows depict the projections of their peculiar motions. The location of the Galactic plane is delineated using O-rich and C-rich Miras from Iwanek et al. (2023), represented by blue and red dots, respectively, while classical Cepheids from Skowron et al. (2019) are indicated by black dots. The presence of the warped disk is evident in the middle panel (for more details, see Skowron et al. 2019; Iwanek et al. 2023). The filled black circle marks the positions of the Sgr dwarf spheroidal galaxy, which is located at a distance of ∼20 kpc (Karachentsev et al. 2004) in the direction of (l, b) = (5°.608, −14°.086). The X–Y plot incorporates the Galactic spiral arm model, based primarily on Reid et al. (2019), as well as an updated structure of the Sgr arm that contains new maser parallax measurements (S. B. Bian et al. 2023, in preparation). The red line in the top panel indicates the intersections between the Sgr orbital plane and the Galactic midplane. A 3D plotly interactive version of this figure is available in the online Journal and at the author's website (https://gongyan2444.github.io/3D/mw-sio.html).

(An interactive version of this figure is available.)

An interactive version of this figure is available in the online journal.