2006A&A...454L..83L

We observed the high velocity outflow originating from NGC 6334 I in several CO transitions with the APEX telescope, with the goal of deriving the physical parameters of the gas. Using an LVG analysis, we studied line ratios between the CO(3-2), CO(4-3), and CO(7-6) data as a function of the density and of the kinetic temperature of the gas. An upper limit on the CO column density is derived by comparison with ¹³CO data. We constrained the temperature to be higher than 50K and the H₂ density to values higher than n∼10⁴cm^–3 towards the peak position in the red lobe, while T>15K and n>10³cm^–3 are derived towards the peak position in the blue lobe. The physical parameters of the outflow, its mass and its energetics, have been computed using the temperatures derived from this analysis. We conclude that high kinetic temperatures are present in the outflow and traced by high excitation CO lines. Observations of high-J CO lines are thus needed to infer reliable values of the kinetic temperatures and of the other physical parameters in outflows.