A Kinematic Analysis of the Giant Molecular Complex W3; Possible Evidence for Cloud-Cloud Collisions that Triggered OB Star Clusters in W3 Main and W3(OH)

W3 is one of the most outstanding regions of high-mass star formation in the outer solar circle, including two active star-forming clouds, W3 Main and W3(OH). Based on a new analysis of the ^12CO data obtained at 38^'' resolution, we have found three clouds having molecular mass from 2000 to 8000 M_⊙ at velocities, -50 km s^-1, -43 km s^-1, and -39 km s^-1. The -43 km s^-1 cloud is the most massive one, overlapping with the -39 km s^-1 cloud and the -50 km s^-1 cloud toward W3 Main and W3(OH), respectively. In W3 Main and W3(OH), we have found typical signatures of a cloud-cloud collision, i.e., the complementary distribution with/without a displacement between the two clouds and/or a V-shape in the position-velocity diagram. We frame a hypothesis that a cloud-cloud collision triggered the high-mass star formation in each region. The collision in W3 Main involves the -39 km s^-1 cloud and the -43 km s^-1 cloud. The collision likely produced a cavity in the -43 km s^-1 cloud having a size similar to the -39 km s^-1 cloud and triggered the formation of young high-mass stars in IC 1795 2 Myr ago. We suggest that the -39 km s^-1 cloud is still triggering the high-mass objects younger than 1 Myr embedded in W3 Main currently. On the other hand, another collision between the -50 km s^-1 cloud and the -43 km s^-1 cloud likely formed the heavily embedded objects in W3(OH) within ∼0.5 Myr ago. The present results favour an idea that cloud-cloud collisions are common phenomena not only in the inner solar circle but also in the outer solar circle, where the number of reported cloud-cloud collisions is yet limited (Fukui et al. 2021, PASJ, 73, S1).