Example spectra and optical depths at l = +29.935°, b = −0.053° (at 46″ resolution). Topmost two panels: 1665 and 1667 MHz absorption features. The fitted Gaussian profiles for the 1665 MHz line (cyan) and 1667 MHz line (orange) are overlaid. Two middle panels: optical depth of the 1665 and 1667 MHz transitions. Second panel from the bottom: emission of ¹³CO (1–0) in main-beam temperature (T_mb), overlaid with a fitted Gaussian profile (red). Lowermost panel: H I optical depth as measured from the absorption spectra. Lower limits (cyan dots) are given for saturated bins. The blue shaded area in the lower four panels denotes the area of the transitions, from which the column densities are determined.