Molecular line mapping of the giant molecular cloud associated with RCW 106 – IV. Ammonia towards dust emission

Here we report observations of the two lowest inversion transitions of ammonia (NH₃) with the 70-m Tidbinbilla radio telescope. The aim of the observations is to determine the kinetic temperatures in the dense clumps of the G333 giant molecular cloud associated with RCW 106 and to examine the effect that accurate measures of temperature have on the calculation of derived quantities such as mass. This project is part of a larger investigation to understand the time-scales and evolutionary sequence associated with high-mass star formation, particularly its earliest stages. Assuming that the initial chemical composition of a giant molecular cloud is uniform, any abundance variations within will be due to evolutionary state. We have identified 63 clumps using SEST Imaging Bolometer Array 1.2-mm dust continuum maps and have calculated gas temperatures for most (78 per cent) of these dense clumps. After using Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire 8.0 μm emission to separate the sample into infrared (IR)-bright and IR-faint clumps, we use statistical tests to examine whether our classification shows different populations in terms of mass and temperature. We find that in terms of log clump mass (2.44–4.12 M_⊙) and log column density (15.3–16.6 cm⁻²), that there is no significant population difference between IR-bright and IR-faint clumps, and that kinetic temperature is the best parameter to distinguish between the gravitationally bound state of each clump. The kinetic temperature was the only parameter found to have a significantly low probability of being drawn from the same population. This suggests that clump radii do not have a large effect on the temperature of a clump, so clumps of similar radii may have different internal heating mechanisms. We also find that while the IR-bright clumps have a higher median log virial mass than the IR-faint clumps (IR-bright: 2.88 M_⊙; IR-faint: 2.73 M_⊙), both samples have a similar range for both virial mass and full width at half-maximum (FWHM; IR-bright: log virial mass = 2.03–3.68 M_⊙, FWHM = 1.17–4.50 km s⁻¹; IR-faint: log virial mass = 2.09–3.35 M_⊙, FWHM = 1.05–4.41 km s⁻¹). There are 87 per cent (40 of 46) of the clumps with masses larger than the virial mass, suggesting that they will form stars or are already undergoing star formation.