ISMGCC: Finding Gas Structures in Molecular Interstellar Medium Using Gaussian Decomposition and Graph Theory

Molecular line emissions are commonly used to trace the distribution and properties of molecular Interstellar Medium (ISM). However, the emissions are heavily blended on the Galactic disk toward the inner Galaxy because of the relatively large line widths and the velocity overlaps of spiral arms. Structure identification methods based on voxel connectivity in PPV data cubes often produce unrealistically large structures, which is the ``over-linking'' problem. Therefore, identifying molecular cloud structures in these directions is not trivial. We propose a new method based on Gaussian decomposition and graph theory to solve the over-linking problem, named ISMGCC (InterStellar Medium Gaussian Component Clustering). Using the MWISP ¹³CO~(1-0) data in the range of 13.5∘ ≤ l ≤ 14.5∘, |b| ≤ 0.5∘, and -100≤ VLSR ≤ +200~km~s⁻¹, our method identified three hundred molecular gas structures with at least 16 pixels. These structures contain $92%$ of the total flux in the raw data cube. Meanwhile, these structures show single-peaked line profiles on more than $93%$ of their pixels. This indicates that the ISMGCC method could distinguish gas structures in crowded regions with minimal flux loss.