Estimating column density from ammonia (1,1) emission in star-forming
  regions
  We present a new, approximate method of calculating the column density of
ammonia in mapping observations of the 23 GHz inversion lines. The temperature
regime typically found in star forming regions allows for the assumption of a
slowly varying partition function for ammonia. It is therefore possible to
determine the column density using only the (J=1,K=1) inversion transition
rather than the typical combination of the (1,1) and (2,2) transitions, with
additional uncertainties comparable to or less than typical observational
error.
  The proposed method allows column density and mass estimates to be extended
into areas of lower signal to noise ratio. We show examples of column density
maps around a number of cores in the W3 and Perseus star-forming regions made
using this approximation, along with a comparison to the corresponding results
obtained using the full two-transition approach. We suggest that this method is
a useful tool in studying the distribution of mass around YSOs, particularly in
the outskirts of the protostellar envelope where the (2,2) ammonia line is
often undetectable on the short timescales necessary for large area mapping.
