I review the major science outcomes to date of the Galactic Census of High- and Medium-mass Protostars (CHaMP), and also report the latest observational results on this unbiased, uniform sample of massive, cluster-forming molecular clumps, based on new mm-wave and IR data. These clouds represent the vast, subthermally-excited population of clumps predicted by Narayanan et al. (2008) to dominate the molecular mass of disk galaxies. Besides confirming their existence, we have presented evidence that these massive clumps probably spend a large fraction (90–95%) of their long lives (possibly up to 100 Myr) in a mostly quiescent, low star formation rate (SFR) state. This is likely ended when a density or internal pressure threshold is crossed, after which vigorous, massive cluster formation consumes the densest gas with a high SFR, dispersing the embedding envelope. New results presented in two other posters at this Symposium include (1) the first analysis of HCN emission from the dense gas (Schap et al.2015), and (2) the first deep photometry of clusters in this sample based on NIR AAT & CTIO data, and on MIR Warm Spitzer IRAC data (Dallilar et al.2015).

The CHaMP project has identified a uniform sample of 303 massive (20–8000 M⊙), dense (200–30,000 cm−3) molecular clumps in a large sector of the southern Milky Way that includes much of the Carina Arm. These are the kinds of clumps that are likely to be the precursors to IRDCs, large stellar clusters, and massive stars. We report new results of the physical conditions in these clouds based on the J=1 → 0 emission at 3mm from the HCN molecule. Analysis of the HCN emission from these clumps reveals that the physical conditions in the gas (i.e., the excitation temperature, optical depth, and column density) do not follow the molecular line emissivity in a straightforward way. This means that large fractions of the molecular material involved in massive cluster formation, while not completely“dark”, are under-luminous and easily missed in certain studies.

The Magellanic Clouds, consisting of the LMC, the SMC and the Bridge offer an ideal laboratory for studying cluster formation in a lower metal abundance environment at an unrivaled closeness to us among external galaxies. It is known that very young populous clusters like R136 are still being formed in the LMC, where populous clusters include more than 10000 stars tightly gravitationally bound. In this talk, I will present mm and sub-mm CO observations of the Magellanic molecular clouds obtained with NANTEN, SEST, and ASTE at spatial resolutions of 5–50pc. I will then use these CO data to identify the parent cloud cores for populous clusters and discuss the cluster formation by comparing the cloud properties with those of the Milky Way.