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'.

本数据集提供了银河系12CO分子云内13CO结构之间的投影角间距与视向速度间距。研究中的12CO分子云和13CO结构均源自《银河系成像卷轴巡天》（Milky Way Imaging Scroll Painting, MWISP）CO巡天项目的CO谱线数据（Su et al. 2019）。115 GHz频段下的半功率波束宽度（half-power beam width, HPBW）约为50角秒。12CO(1-0)谱线的速度分辨率约为0.16 km s⁻¹，13CO和C18O谱线的速度分辨率约为0.17 km s⁻¹。12CO谱线的均方根噪声（root mean square, rms）约为0.5 K，13CO谱线的均方根噪声约为0.3 K。12CO分子云和13CO结构均通过基于密度的带噪声应用空间聚类（Density-based Spatial Clustering of Applications with Noise, DBSCAN）算法提取（Ester et al. 1996; Yan et al. 2021; Yuan et al. 2022）。已公开的18190个12CO分子云的提取谱线数据，以及2851个12CO分子云内部的13CO提取谱线数据，可通过DOI:10.57760/sciencedb.j00001.00427获取。本研究使用最小生成树（minimal spanning tree, MST）算法，将单个12CO分子云内的所有13CO结构连接起来，同时最小化这些13CO结构之间的总间距。13CO结构之间的观测角间距为其真实三维间距在天球平面上的投影，通过两个13CO结构的银河中心坐标的欧几里得距离计算得到。此处的银河中心坐标指提取得到的13CO结构内所有体素的银河坐标加权平均值，权重为对应的13CO(1-0)谱线强度。中心速度则为13CO结构内所有体素的视向速度加权平均值，权重为13CO谱线强度。视向速度间距由这些相连的13CO结构的中心速度之差确定。在2851个包含13CO结构的12CO分子云中，有443个分子云包含2个13CO结构，560个分子云包含多于2个的13CO结构。对于这1003个包含双个或多个13CO结构的12CO分子云，本数据集上传了展示其内部13CO结构分布以及连接这些结构的最小生成树的图像。此外，还上传了包含每个12CO分子云内13CO结构之间投影角间距和视向速度间距的表格。表格命名为`cloud_ID_separation_tree_N.txt`，其中`ID`为DOI:10.57760/sciencedb.j00001.00427发布的星表中的分子云ID，`N`为该12CO分子云中包含的13CO结构数量。每个表格的表头字段说明如下：`sepa_angular`代表投影角间距，单位为角分（arcmin）；`sepa_velocity`代表视向速度间距，单位为km/s；`structure_i`与`structure_j`为对应该间距的两个相连13CO结构的编号。所有表格均存放于`separation_tables_txt`文件夹中。图像命名为`cloud_ID_13co_tree.pdf`，其中`ID`同样为分子云ID。每张图像包含两个面板：左面板的色标代表12CO分子云内部13CO谱线发射的速度积分强度分布，白色和品红色轮廓线分别表示12CO分子云和13CO结构的边界；右面板展示了连接该12CO分子云内部13CO结构的最小生成树，每个节点代表一个13CO结构，标注的编号与表格中`structure_i`和`structure_j`的编号相对应。所有图像均存放于`13costrs_MST_figures`文件夹中。