On the Spatial Distribution of 13CO structures within 12CO molecular clouds

We present the projected angular separations and radial velocity separations between 13CO structures within 12CO molecular clouds. The 12CO clouds and 13CO structures are identified from CO lines in the Milky Way Imaging Scroll Painting (MWISP) CO survey (Su et al. 2019). The half-power beam width (HPBW) at 115 GHz is about 50 arcsec. The velocity separation is about 0.16 km s-1 for 12CO(1-0) and 0.17 km s-1 for 13CO and C18O lines. An rms noise level of ~ 0.5 K for the 12CO lines and ~ 0.3 K for the 13CO lines are achieved. The 12CO clouds and 13CO structures were extracted using the Density-based Spatial Clustering of Applications with Noise (DBSCAN) algorithm (Ester et al. 1996; Yan et al. 2021; Yuan et al. 2022). The extracted 12CO line data for 18,190 12CO clouds and the extracted 13CO line data within the 2851 12CO clouds are available at DOI:10.57760/sciencedb.j00001.00427. We use the minimal spanning tree (MST) algorithm to connect the whole 13CO structures in a single 12CO cloud together, while minimizing the total sum of the spacings between these 13CO structures. The observed angular separations between 13CO structures are the projection of their true 3-D spacings onto the plane of the sky, which are calculated as the euclidean distances between the central Galactic coordinates of 13CO structures. Their central Galactic coordinates are the averaged Galactic coordinates over all voxels within extracted 13CO structures, weighted by the corresponding 13CO(1-0) line intensities. The central velocity is the averaged radial velocity over all voxels within the extracted 13CO structure, weighted by the 13CO line intensities. The radial velocity separations are determined by the differences between the central velocities of these connected 13CO structures.Among the 2851 12CO clouds harboring 13CO structures, 443 clouds have double 13CO structures and 560 clouds have multiple (larger than two) 13CO structures. For the 1003 12CO clouds having double or multiple 13CO structures, we upload the figures showing the distribution of their internal 13CO structures and the computed MSTs connecting the 13CO structures. Moreover, the tables including the projected angular separations and radial velocity separations between the 13CO structures with each 12CO cloud are also uploaded.The tables are named 'cloud_ID_separation_tree_N.txt', and 'ID' is the molecular cloud ID in the catalog published in DOI:10.57760/sciencedb.j00001.00427. 'N' is the number of 13CO structures in this 12CO cloud. For the header in each table, 'sepa_angular' represents the projected angular separation, and its unit is arcmin; 'sepa_velocity' means the radial velocity separation, and its unit is km/s; 'structure_i' and 'structure_j' is the No. for the two connected 13CO structures corresponding to the separation. These tables are in the file 'separation_tables_txt'. The figures are named 'cloud_ID_13co_tree.pdf', ID also is the molecular cloud ID. In each figure, the colormap in the left panel represents the distribution of the velocity-integrated intensities of 13CO line emission within a 12CO cloud, the white and magenta contours indicate the boundaries of 12CO cloud and 13CO structures; in the right panel, we show the minimal spanning tree connecting the internal 13CO structures over a 12CO cloud, each node represent a 13CO structure, the noted No. are corresponding to the 'structure_i' and 'structure_j' listed in the table. The figures are in the file '13costrs_MST_figures'.