N₂H⁺ column density profile (top panel) and simulated J = 4–3 line emission (middle and bottom panels) for the N₂H⁺ distributions predicted by the simple chemical model with CO and N₂ abundances of 3 × 10^-6 (model CH; red lines) and a model incorporating only freeze-out and desorption (model FD; black lines). Integrated line intensity profiles are shown after convolution with a beam (middle panel) or a beam (bottom panel). Observations by Q13 are shown in gray in the middle panel with the 3σ-error depicted in the lower right corner. The vertical gray line marks the position of the observed emission peak. The vertical blue line indicates the position of the midplane CO snowline inferred from these observations by Q13, while the red line indicates the location of the midplane CO snowline in the models.