2025MNRAS.542...52Z

Kinematic information is crucial for understanding the evolution of complex systems, such as interstellar gas. Obtaining full 3D kinematic information is a vital final step for modelling and interpretation. Molecular clouds (MCs) are nurseries where stars are born. Stars at a very early stage, such as young stellar objects (YSOs), inherit the spatial and kinematic structure of the gas patches in which they originate. In this paper, we combine measurements of radial velocities towards the gas and the kinematic information of YSOs from Gaia DR3 to derive 3D velocities of a sample of YSO-MC complexes at d $\lesssim$ 3.5 kpc from the Sun. We find that the molecular interstellar medium traced by the YSO-MC complexes generally follows Galactic rotation, with an additional peculiar velocity of 8.6 km s$^{-1}$. The random motion of these complexes in the Galactic x-y-plane is more energetic than motion along the z-direction. A catalogue containing the 3D velocities of the YSO-MC complexes in various reference frames is available, and the distances and 3D velocities of well-known MCs are presented. Our results establish the foundation for exploring the interplay between the Galaxy, the molecular interstellar medium, and star formation.