Determination of 3D structures of molecular clouds in high-resolution mm images

Official URL: https://dx.doi.org/10.1007/978-3-032-02232-5_1

We investigate the line-of-sight molecular clouds toward the black hole transient 4U 1630–47 using high-resolution 12CO (J=1–0) observations from the Atacama Pathfinder Experiment (APEX). Motivated by the need to resolve overlapping velocity features in narrow field data, we developed a specialized four-step pipeline—Gaussian-based peak detection, data segmentation, Otsu thresholding, and a modified Mean Shift clustering algorithm—to reconstruct cloud structures in three dimensions. In doing so, we address the distance ambiguity observed in earlier low-resolution CO studies, particularly for molecular clouds that produce the dust scattering halo of 4U 1630–47. This methodology reveals 15 distinct molecular clouds along the line of sight and clarifies their morphological overlaps, thereby enhancing our understanding of the dust-scattering geometry. Moreover, our framework extends beyond 4U 1630–47, providing a robust approach for analyzing similar dust scattering halos and distinguishing complex cloud environments in other high-resolution, narrow-field observations. In particular, these results further constrain the distance to 4U 1630–47, supporting more accurate physical and geometric modeling of the system.