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, and includes two active star-forming clouds: W3 Main and W3(OH). Based on a new analysis of the (CO)-C-12(J=2--1) data obtained at 38 '' resolution, we have found three clouds that have molecular masses from 2000 to 8000M(circle dot) at velocities -50kms(-1), -43kms(-1), and -39kms(-1). The -43kms(-1) cloud is the most massive one, overlapping with the -39kms(-1) cloud and the -50kms(-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 -39kms(-1 )cloud and the -43kms(-1) cloud. The collision likely produced a cavity in the -43kms(-1) cloud that has a size similar to the -39kms(-1) cloud and triggered the formation of young high-mass stars in IC 1795 2Myr ago. We suggest that the -39kms(-1) cloud is still triggering the high-mass objects younger than 1Myr currently embedded in W3 Main. On the other hand, another collision between the -50kms(-1) cloud and the -43kms(-1) cloud likely formed the heavily embedded objects in W3(OH) within similar to 0.5Myr 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).