Degeneracy in n_pre and v_s. To illustrate this issue, the observed CO and H₂ 0–0 S(3) transitions of the pixel [−1, 2] are shown in the left and right plots along with three different shock models (“M1” in red: n_pre = 10⁴ cm⁻³ and v_s = 28 km s⁻¹; “M2” in green: n_pre = 5 × 10⁴ cm⁻³ and v_s = 7.5 km s⁻¹; “M3” in blue: n_pre = 10⁶ cm⁻³ and v_s = 4 km s⁻¹). For both plots, dark and light gray colors are used to represent detections and nondetections, and = 0 and Ω ~ 0.1 are adopted for the three shock models.