Allingham et al. have used the ATCA to study the structure and temperature distribution within high-mass star-forming clumps in our Galaxy as part of the Curated ATCA Census of High-Mass Clumps (CACHMC) Legacy Project. They imaged a number of ammonia (NH ₃ ) lines, the H ₂ O maser line at 22.2 GHz, several methanol CH ₃ OH lines and hydrogen and helium recombination lines. In addition, 22- and 24-GHz radio continuum emission was also imaged. The NH3 lines probe the optical depth and gas temperature of compact structures within the clumps. The H2O maser pinpoints the location of shocked gas associated with star formation. The recombination lines and the continuum emission trace the ionised gas associated with hot OB stars.

The figure above shows a combined plot of transition lines at the target position in the “Nessie” nebula. Lines are all shown at the same scale (except for the H ₂ O maser line, shown in yellow, whose emission has been down-scaled by 100 times) and have been offset from each other by 0.2 Jy/beam. The data is aligned to radial velocity: a vertical bar has been added at the target’s systemic velocity (−39.58 km/s) to aid visual interpretation. Line colours distinguish the different molecules and atoms.