Integrated intensity maps of ¹³CO (1–0) (a), C¹⁸O (1–0) (b), C¹⁷O (1–0) (c), ¹³CO (2–1) (d), C¹⁸O (2–1) (e), and C¹⁷O (2–1) (f). Their integrated velocity ranges are [6.5, 10] km s⁻¹ for ¹³CO (1–0), C¹⁸O (1–0), ¹³CO (2–1), and C¹⁸O (2–1), [7.5, 9] km s⁻¹ for C¹⁷O(1–0), and [6, 10] km s⁻¹ for C¹⁷O (2–1). The contours start at 0.4 K km s⁻¹ with a step of 0.4 K km s⁻¹ for ¹³CO (1–0), C¹⁸O (1–0), ¹³CO (2–1), and C¹⁸O (2–1). For the two C¹⁷O maps, the contours start at 3σ with a step of 3σ, where 1σ = 0.08 K km s⁻¹ for C¹⁷O (1–0) and 1σ = 0.06 K km s⁻¹ for C¹⁷O (2–1). The color bar represents the C¹⁸O (1–0) and C¹⁸O (2–1) integrated intensities in units of K km s⁻¹. The ¹³CO (1–0), ¹³CO (2–1), C¹⁷O (1–0), and C¹⁷O (2–1) maps have been scaled by 0.4, 0.5, 3, and 3 to match the color bar. Panel d: the red dashed line is used to divide the Serpens filament into two parts, NW and SE, and the blue line represents the crest of the Serpens filament extracted in the corresponding H₂ column density map (Gong et al. 2018). In all panels, the (0, 0) offset corresponds to α_J2000 = 18^h28^m50.^s4, δ_J2000 = 00°49′58.′′72, the three green pluses indicate the positions of the three embedded YSOs, emb10, emb16, and Ser-emb 28 (see Enoch et al. 2009, and Fig. 1), and the white crosses mark the positions of the seven dust cores (see Enoch et al. 2007, and Fig. 1).