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Abstract
If a giant molecular cloud (GMC) begins with the same molecular abundances throughout, then any changes observed between different clumps within that GMC are due to its evolutionary stage. By studying how high-mass stars form from clumps, we are able to identify how they shape and are shaped by their environment.
We study two different GMCs: the G333 GMC and cloud C of the Vela Molecular Ridge (VMR-C). For the G333 GMC, we enhanced a 3-mm molecular line survey conducted on the Mopra radio telescope by including ammonia (temperature) observations targeted towards dust clumps with the Tidbinbilla 70-m radio telescope. For the VMR-C GMC, we conducted a 12-mm molecular line survey on the Mopra radio telescope. We detected emission for ammonia, cyanoacetylene, cyanobutadiynene, and the water maser line. We modelled the spectral energy distribution for the five dust clumps identified by the water maser emission. We studied the morphology and turbulent properties of both GMCs using molecular transitions from carbon monoxide and its isotopologues, hydrogen cyanide, hydrogen isocyanide, formylium, and diazenylium.
In G333 GMC, we find evidence that the clumps identified by molecular emission are substantial in size. Clumps with star formation signs are generally warmer and have larger turbulent line widths. We find evidence of radially triggered star formation in the G333 GMC: infrared clumps without obvious signs of star formation are found preferentially further away from known sites of star formation.
We highlight the differences between star formation in the two GMCs by analysing the probability distribution function (PDF) of the molecular gas. Both GMCs have a hierarchical, turbulence driven component, and a gravitationally bound component; with less gravitationally bound gas in the VMR-C GMC. We trialled a new technique: the PDF analysis of molecular lines and show that it can identify real differences between molecular clouds.