Spatial distributions of different molecular species, labeled in the lower right of each panel, over the Serpens filament. Panel a: Herschel H₂ column density image. The contours are H₂ column densities of 4 × 10²¹ cm⁻² and 6 × 10²¹ cm⁻². This region is divided by the two white dashed lines into three individual regions which are labeled NW (northwest), SE (southeast), and EX (extended). Panel b: C¹⁸ O (1–0) intensity map integrated from 7.4 to 8.7 km s⁻¹. The contours start at 0.30 K km s⁻¹ (5σ), and increase by 0.18 K km s⁻¹ (3σ). Panel c: HCO⁺ (1–0) intensity map integrated from 6.5 to 9.5 km s⁻¹. The contours start at 0.27 K km s⁻¹, and increase by 0.27 K km s⁻¹. Panel d: HNC (1–0) intensity map integrated from 7.0 to 9.0 km s⁻¹. The contours start at 0.24 K km s⁻¹, and increase by 0.24 K km s⁻¹. Panel e: HCN (1–0) intensity map integrated from 0 to 1.6 km s⁻¹, from 7.0 to 8.6 km s⁻¹, and from 11.8 to 13.4 km s⁻¹ relative to the frequency of the F = 2–1 hyperfine structure component. The contours start at 0.27 K km s⁻¹, and increase by 0.27 K km s⁻¹. Panel f: N₂H⁺ (1–0) intensity map integrated from 6.5 to 9.5 km s⁻¹. The contours start at 0.30 K km s⁻¹, and increase by 0.30 K km s⁻¹. Panel g: CS (2–1) intensity map integrated from 7.0 to 9.5 km s⁻¹. The contours start at 0.18 K km s⁻¹, and increase by 0.18 K km s⁻¹. Panel h: CH₃OH (2₀ –1₀) intensity map integrated from 7.5 to 8.8 km s⁻¹. The contours start at 0.12 K km s⁻¹, and increase by 0.12 K km s⁻¹. In all panels, the (0, 0) offset corresponds to α_J2000 = 18^h28^m49.^s642, δ_J2000 = 00°50′01.′′08, and the three blue crosses give the positions of the three embedded YSOs (see also Fig. 1). The beam size is shown in the lower right of each panel.