3D Morphology and Motions of the Canis Major Region from Gaia DR3

The Canis Major (CMa) region is known for its prominent arc-shaped morphology, visible at multiple wavelengths. This study integrates molecular gas data with high-precision astrometric parameters of young stellar objects (YSOs) from Gaia DR3 to provide the first three-dimensional (3D) insights into the dynamical evolution and star formation history of the CMa region. By utilizing the average distances and proper motions of the YSOs as proxies for those of the molecular clouds (MCs), we confirm the presence of a slowly expanding shell-like morphology in the CMa region, with the estimated radius of 47$\pm$11 pc and expansion velocity of 1.6$\pm$0.7 km/s. Further, the dynamical evolution of the shell supports its expansion, with an expansion timescale of $\sim$4.4 Myr obtained by the traceback analysis assuming constant velocities. Finally, a momentum estimate suggests that at least 2 supernova explosions (SNe) are needed to power the observed expanding shell, reinforcing the previous hypothesis of multiple SNe events. This study effectively combines the CO data with the astrometric data of YSOs from Gaia, offering significant support for the future studies on the 3D morphology and kinematics of MCs.