From left to right, log of the optical depth of ¹³CO (), log of the 3σ column density of H₂ in cm⁻², and log of the upper limit in the column density of H₂ in cm⁻². Overlaid are the radio contours at 1420 MHz in units of brightness temperature at 4.8, 5.0, 5.5, and 6.0 K. The difference between the middle and right columns is that for the middle column the N(H₂) was calculated for the regions where the peak temperature of ¹³CO was 3 times or more the rms value for that pixel (i.e. right panel in Fig. A.1), whereas for the right column the peak ¹³CO was within 3σ, resulting in only an upper limit. Top panels: distant component (− 27.5 to − 15.5  km s⁻¹). Middle panels: close component (− 8.5 km s⁻¹ to − 1.0 km s⁻¹). Bottom panels: entire velocity space of our observations.