Velocity-integrated intensity maps (T_mb scale; color bar in units of K km s⁻¹) of H₂CO 3₀₃ −2₀₂ (left), 3₂₂−2₂₁ (center left), 3₂₁−2₂₀ (center right), and averaged 3₂₂−2₂₁ and 3₂₁−2₂₀ (right), integrated from V_LSR = −10 to 4 km s⁻¹ of the DR21 filament. Contour levels are from 4.8 to 12K km s⁻¹ with steps of 1.8K km s⁻¹ and from 12 to 59 K km s⁻¹ with steps of 3.6K km s⁻¹ for H₂CO3₀₃−2₀₂, and from 1.7 to 4.4K km s⁻¹ with steps of 0.66K km s⁻¹ and from 4.3 to 21.2 K km s⁻¹ with steps of 1.3K km s⁻¹ for H₂CO 3₂₂ −2₂₁, 3₂₁−2₂₀, and combined 3₂₂−2₂₁ and 3₂₁−2₂₀ .The locations of source names are taken from Davis et al. (2007), Reipurth & Schneider (2008), and Ching et al. (2022).