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To develop our understanding of the earliest stages of massive star formation, we have recently undertaken an imaging survey of ammonia
with the ATCA toward a sample of 90 sources traced by 6.7GHz methanol maser emission -- an excellent indicator of early massive star formation (Longmore et al. 2007A). With LVG modelling of multiple ammonia transitions, we were able to calculate reliable gas column densities and kinetic temperatures to separate the thermal and
non-thermal contribution to the measured linewidth and hence investigate turbulent injection (Longmore et al. 2007B). Making two reasonable assumptions, first, that the cores will increase in temperature as the internal powering sources `switch on' and second, that these internal heat sources will inject turbulence into the gas through e.g. outflows, we built a coherent picture of the core's evolutionary stage. In this way, we have isolated a sample of massive cores with very low temperature and little turbulence, which we
conclude are massive protostellar cores in their earliest stages of evolution.
From simultaneously observed 24 GHz continuum emission, we were also able to determine which of these regions are associated with free-free
emission from gas ionised by an existing massive star. Surprisingly, we found many of the 24 GHz continuum sources at locations devoid of 8
GHz continuum emission (reported from previous surveys, e.g. Walsh et al 1998). Comparing the 8 & 24\,GHz data sets, we concluded that either: (i) the continuum emission is significantly extended and thus resolved/filtered-out by the more extended array configuration of the previous 8 GHz observations, or, (ii) the continuum emission has a spectral index ~ 2 and is thus optically thick between 8 and 24 GHz characteristic of hyper-compact HII regions. Given that the 24
GHz-only sources are always coincident with both methanol maser and ammonia emission, the latter scenario seems more likely.
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