Panel a: LSR velocity map similar to Fig. 4b but overlaid with the H₂ column density contours which represent 4 × 10²¹ cm⁻² and 6 × 10²¹ cm⁻². Source B is marked with the red circle, and the three black crosses give the positions of the three embedded YSOs, em10, em28, and em16. Panel b: column density profile along the crest of the Serpens filament indicated by the blue line in panel a. The spatial resolution is ~0.08 pc. The offset increases from south to north. The red line represents a sinusoidal fit to the profile within the offset range of 1.0–1.4 pc. A sinusoidal orange line is created to better visualize the variation at a large scale. Panel c: similar to panel b, but for the C¹⁸ O (1–0) velocity. The four red arrows correspond to the velocity gradients in Fig. 4b, indicated there by black arrows. Panel d: similar to panel c, but for the C¹⁸ O (1–0) linewidths. In panels b–d, the red dashed lines indicate the positions of Source B and the YSO emb28.