Three-dimensional distribution of hydrogen fluoride gas toward NGC6334 I
  and I(N)
  Aims. We investigate the spatial distribution of a collection of absorbing
gas clouds, some associated with the dense, massive star-forming core NGC6334
I, and others with diffuse foreground clouds. For the former category, we aim
to study the dynamical properties of the clouds in order to assess their
potential to feed the accreting protostellar cores.
  Methods. We use spectral imaging from the Herschel SPIRE iFTS to construct a
map of HF absorption at 243 micron in a 6x3.5 arcmin region surrounding NGC6334
I and I(N).
  Results. The combination of new, spatially fully sampled, but spectrally
unresolved mapping with a previous, single-pointing, spectrally resolved HF
signature yields a 3D picture of absorbing gas clouds in the direction of
NGC6334. Toward core I, the HF equivalent width matches that of the spectrally
resolved observation. The distribution of HF absorption is consistent with
three of the seven components being associated with this dense star-forming
envelope. For two of the remaining four components, our data suggest that these
clouds are spatially associated with the larger scale filamentary star-forming
complex. Our data also implies a lack of gas phase HF in the envelope of core
I(N). Using a simple description of adsorption onto and desorption from dust
grain surfaces, we show that the overall lower temperature of the envelope of
source I(N) is consistent with freeze-out of HF, while it remains in the gas
phase in source I.
  Conclusions. We use the HF molecule as a tracer of column density in diffuse
gas (n(H) ~ 10^2 - 10^3 cm^-3), and find that it may uniquely trace a
relatively low density portion of the gas reservoir available for star
formation that otherwise escapes detection. At higher densities prevailing in
protostellar envelopes (>10^4 cm^-3), we find evidence of HF depletion from the
gas phase under sufficiently cold conditions.
