(a) Three-color image showing the integrated intensity of the three velocity components, 5–20 km s⁻¹ (blue), 32–40 km s⁻¹(green), and 42–58 km s⁻¹ (red), associated with SDC13, identified from the IRAM 30 m C¹⁸O (1–0) data with a resolution of 24.″6 and an rms noise of 0.17 K. The white contours are the 100, 300, and 500 mJy beam⁻¹ JCMT 850 μm continuum, and the thick white line marks the arc-like magnetic field structure as shown in Figure 2. The green component is consistent with the “Y-shape” SDC13 HFS. The yellow segments are the larger than 2σ magnetic field segments. The blue component reveals four filamentary arms converging to the clump within the SDC13 filament S, consistent with the filaments identified in the 850 μm dust continuum. One of these arms extending to the central hub is likely aligned with the arc-like magnetic field structure. The red component connects the eastern to the SDC13 central hub through a bridge. (b) Three-color image showing the three GMCs, SDG013.178-0.0950 (blue), SDG012.840-0.2041 (green), and SDG013.222+0.0076 (red) from the APEX ¹³CO (2-1) data with a resolution of 30″ and an rms noise of 1 K, which spatially overlap with SDC13 and which are also associated with the three C¹⁸O components displayed in the (a). The yellow box labels the outer boundary of (a). SDG012.840-0.2041 is consistent with the large-scale north–south filament seen by Herschel in Figure 12. Most of the compact clouds detected in the JCMT 850 μm continuum are located near the edge or the boundary of these GMCs, either perpendicular or parallel to the large-scale PLANCK magnetic field.