The Millimetre Astronomy Legacy Team 90 GHz (MALT90) survey aims to characterise the physical and chemical evolution of high-mass star-forming clumps. Exploiting the unique broad frequency range and on-the-fly mapping capabilities of the Australia Telescope National Facility Mopra 22 m single-dish telescope1, MALT90 has obtained 3′ × 3′ maps towards ~2 000 dense molecular clumps identified in the ATLASGAL 870 μm Galactic plane survey. The clumps were selected to host the early stages of high-mass star formation and to span the complete range in their evolutionary states (from prestellar, to protostellar, and on to $\mathrm{H\,{\scriptstyle {II}}}$ regions and photodissociation regions). Because MALT90 mapped 16 lines simultaneously with excellent spatial (38 arcsec) and spectral (0.11 km s−1) resolution, the data reveal a wealth of information about the clumps’ morphologies, chemistry, and kinematics. In this paper we outline the survey strategy, observing mode, data reduction procedure, and highlight some early science results. All MALT90 raw and processed data products are available to the community. With its unprecedented large sample of clumps, MALT90 is the largest survey of its type ever conducted and an excellent resource for identifying interesting candidates for high-resolution studies with ALMA.

Submillimeter dust continuum emission traces high molecular column densities and, thus, dense cloud regions in which new stars are forming. Surveys of the Galactic plane in such emission have the potential of delivering an unbiased view of high-mass star formation throughout the Milky Way. The location of the APEX telescope on the Chajnantor plateau in Chile is ideally suited for mapping the inner Galaxy. ATLASGAL, The APEX Telescope Large Area Survey of the Galaxy at 870 μm, is a survey of the Galactic plane using the Large APEX Bolometer Camera (LABOCA), in the Galactic longitude and latitude ranges of  ±60 and  ±1.5°, respectively. This survey is providing an unbiased sample of cold dusty clumps in the Galaxy at submillimeter wavelength and a variety of molecular line follow-up observations have been started to characterize the physical and chemical conditions in the newly found clumps. Here, first results from this survey and its follow-up programs are described.

We show how the expansion of classical Galactic Hii regions can trigger massive-star formation via the collect & collapse process. We give examples of this process at work. We suggest that it also works in a turbulent medium.

Various physical processes are believed to trigger star formation on the borders of Galactic HII regions. Among these, the collect & collapse process is particularly attractive as it allows the formation of massive objects (single stars or clusters). In order to identify specific cases of this way of triggering star formation we are carrying out a multi-wavelength study of Galactic HII regions that exhibit signposts of massive-star formation at their borders. Hereby, we present two typical examples of such sources and discuss the results in the framework of the collect and collapse process, which seems to be at work as the major triggering agent in these two cases.

The Large Magellanic Cloud (LMC) HII region N159A is shown to be a group of ionized regions, some of which overlap, rather than a single HII region. There are at least 11 stars earlier than B2 in this region

A nebular photometer equipped with a scanning Fabry-Perot interferometer has been used at the ESO 50-cm telescope to observe about 50 HII regions of the LMC (Caplan and Deharveng, 1983). This instrumentation gives the profiles of the observed lines, thus allowing discrimination against unwanted continuum and line emission. The integrated fluxes were measured with a 4.9′ diaphragm, to facilitate comparison with the 6-cm radio continuum fluxes obtained by McGee et al. (1972) with a similar resolution. Nebular reddening, from the Hα/Hβ ratio, is greatest for the 30 Doradus Nebula. Relatively high reddening was also observed for the following zones: N159 (at the border of the largest HI-molecular complex of the LMC) and N160; N79, N81 and N83; N48; N64. Reddening is rather low towards other HII regions, especially for those in the bar and for large bubble-shaped regions.

Tenorio-Tagle (1979) first proposed the idea of a third dynamical phase, the champagne phase, following the formation and expansion phases of an HII region; the idea was further explored by Bodenheimer et al. (1979) and Tenorio-Tagle et al. (1979). The champagne phase begins when the high pressure gas of an HII region formed inside a molecular cloud reaches the edge of the cloud and bursts into the lower pressure, low density, intercloud medium. One important implication of the model is the prediction of an enormous enhancement of the rate of erosion of the molecular cloud by the ionising radiation of hot stars, which begins as soon as the process of the decrease of the gas density between the star and the cloud is started. The proportion of hydrogen molecules eroded by ionising photons may reach about 10-2. The mass eroded may exceed the mass of the ionised gas in the case where the ionisation front reaching the edge of the cloud is of D-type. Additional mechanisms (for instance stellar winds), if at work, may even increase the efficiency of the mechanism.