Comparison of the velocity profile of the dense-gas lines (HCN(5-4) in blue solid line and HCO⁺(5-4) in red dashed line, and other gas tracers (CO(3-2) in green dotted line and [CI](1-0) in yellow dot-dash line. We plotted the channel RMS uncertainties of HCN(5-4). HCO⁺(5-4) has similar channel uncertainties (not plotted). ¹²CO and [CI] have a much better S/N and their uncertainties can be neglected. We normalized all the lines to have ∫S_ν dν = 500 Jy km s⁻¹. With this normalization, the peak flux of a rectangular line with a typical 500 km s⁻¹ width is unity.