In using ammonia to determine cloud densities and kinetic temperatures, one takes advantage of the many observable lines associated with a single inversion transition. The basic idea is to alter the guessed density and temperature until the observed spectrum is reproduced. In this section, we shall explore this method in some detail, as the molecule has played a key role in determining the properties of dense cores.

1 When observing an external galaxy, the telescope beam usually contains many unresolved clouds. The line width, set by the intercloud velocity, is much greater than A Vr for a single object. We assume, however, that these entities are so sparsely distributed that they do not shadow one another. Then the integrated antenna temperature is what it would be for a collection of static clouds, with the same total column density. Thus, our scaling argument for X still holds.


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