SIMBAD references

We present fully sampled spectral line maps of the Orion Bar region observed simultaneously in the CN N=3-2 and CS J=7-6 rotational transitions with the JCMT at an angular resolution of 14''. We find that the CN emission specifically traces an intermediate cloud layer located between the peaks of vibrationally excited H₂ and HCO⁺ emission located closer to the ionization front, and CS emission originating closer to the cloud core. By comparing the observed spatial displacement of CN and CS emission with PDR models we infer a density of ∼2x10⁵cm^–3 for these cloud layers. This value is in agreement with the results of an escape probability radiative transfer analysis of our CN and CS line observations. We conclude that the observed distribution of H₂/CN/CS is consistent with chemical stratification in an edge-on PDR in which high density gas (∼2x10⁵cm^–3) is distributed homogeneously.