[A] NANTEN maps of a section of the Milky Way, showing a number of distant, high-mass, dense molecular clouds in the constellation of Carina. The colours and contours show that the two ‘dense-gas tracers’ C18O and HCO+ do not precisely trace the same gas, presumably due to physical and chemical variations in conditions inside the clouds. [B] CHaMP spectrum of N2H+ line observed at Mopra from one of these star-forming clouds, showing the broad, blended profiles typical of high-mass star formation. [C] Mopra N2H+ spectrum from a nearby, low-mass cloud in Vela. Note in this case how the hyperfine components of the spectrum are easily separated.

Our own galaxy, the Milky Way, is a vast ecosystem of stars. Not a biological one like the Earth’s, but a physical and chemical one. From the spaces between the stars, gas and dust collect under their own gravity to form new stars, which live the majority of their lives burning nuclear fuel at their centres. When this fuel runs out, their death throes return a large fraction of their material, enriched in heavy elements by their nuclear fires, to interstellar space, thus beginning the cycle over again.

The beginning of this cycle, the formation of stars, is still somewhat of a mystery, especially for stars which are several times more massive than our Sun, or for large clusters of stars. How do such large stars assemble themselves, individually and in clusters? A simple theory would predict massive clusters could not be as tightly packed as we see. Do massive stars drive off their nascent gas in the same way as low-mass stars? Do they have similar, or any, solar systems? The mysteries of massive star formation are important since these stars, while few in number, are a major part of the engine driving the Galactic ecology. Their impressive energy output heats and stirs large tracts of the Galaxy, while their nuclear cauldrons ensure there are plenty of heavy elements in available for future generations of stars to form rocky planets and solar systems. In contrast, the formation of isolated low-mass (or Sun-like) stars is much more common than massive star formation, and a little better understood; however we still lack details about the prevalence of solar systems, the formation of planets, and the clearing of the stars’ gaseous cocoons.

We have begun 2 major projects in 2004 in order to systematically address some of these questions. Using the Mopra dish of the Australia Telescope, CHaMP is collecting a large database of properties of medium- and high-mass star formation throughout the Milky Way by looking at different tracers of dense interstellar gas. In collaboration with Yoshi Yonekura at Osaka Prefecture University and members of the NANTEN group at Nagoya University, we will be able for the first time to build a reliable picture of the typical evolution of these rare but powerful engines of galactic ecology. The second large survey, also primarily using the Mopra radio telescope in collaboration with Tyler Bourke and Phil Myers of Harvard University and others, is part of the Spitzer Space Telescope Legacy Program ‘C2D - From Cores to Disks’. This project is similarly compiling detailed and uniform data on low-mass star forming clouds in our local Galactic neighbourhood.

We obtained our first comprehensive data for both projects at Mopra last winter (see figure), and are scheduled for much more time this coming winter (2005). Analysis of the data obtained so far is ongoing, and has already produced some intriguing results, which we are preparing for publication.

Peter Barnes