We have analyzed new CO ( J = 1–0 ) data in the region of a reflection nebula NGC 2023 with a particular focus on the detailed kinematical properties of the molecular gas .
The results show that there are two velocity components which indicate signatures of dynamical interaction revealed at a high resolution of 19 \arcsec ( = 0.04 pc ) .
Based on the results we propose a hypothesis that two clouds collided with each other and triggered the formation of the B1.5 star HD 37903 in addition to 20 lower mass stars in two small clusters with a size of 2 pc .
Although the previous study favored a scheme of triggering by the H ii region ( e.g. , [ Mookerjea et al .
( 2009 ) ] ) , the present results show that the effect of the H ii region is limited only to the surface of the molecular cloud , and does not contribute to the gas compression and star formation .
The present results lend support for the dominant role of cloud-cloud collision in forming high mass stars in addition to \sim 20 lower mass stars , which are also likely formed by the collision .
The present case suggests all the high mass stars in the Orion region are formed by cloud-cloud collision .