We present the highest angular resolution (~19") image of the
12CO(J=1-0) line toward the almost entire area of the Cygnus-X active
star-forming region taken with the FOREST receiver installed on the Nobeyama 45-m telescope.
The giant molecular clouds (GMCs) of the Cygnus-X
North and South are resolved with a resolution of ~0.13 pc. Molecular
filaments are clearly found in the North GMC, whereas the South GMC
rather consists of a diffuse extended gas. The both GMCs are clearly
divided into two velocity components, one at -3 km s-1 and the other
at 8 km s-1, and these components show spatially complementary
distribution to each other in the GMC scale. In order to test the
complementarity of the gas distributions quantitatively, an evaluation
method based on the degree of anticorrelation was applied (e.g.,
Fujita et al. 2021). The results of the analysis show the correlation
coefficient is <-0.3 for the entire GMCs, which supports a cloud
collision of the GMC scale. In addition, the correlation coefficient
is found to be smaller at the region around the evolved HII regions.
The values are ~-0.6 for DR23, DR 20, and DR12, and ~-0.4 for
G081.5+00.6. These excesses of the correlation coefficient around the
HII regions suggest the colliding event of molecular clouds plays an
important role in formations of individual stellar clusters.
The DR21 and W75N regions are also known as regions where high-mass star formation is triggered by cloud-cloud collisions (Dobashi et al. 2019). However, in our study we did not find a clear complementary distribution between two velocity components around the clusters. Instead, we found a bridging structure connecting the interacting candidates, indicating that the collision is still ongoing and the regions are in a younger stage compared to other regions.