Abstract
We present ISOCAM observations (5–17 μm) of the HST M 16 field, including the striking elephant trunk structures. The spectroscopic data have been obtained using the ISOCAM-CVF low-resolution mode, having a spectral resolution of ~40 () and a pixel size of 6″. The spectra show a combination of Unidentified Infrared Band (UIB) emission centred at 6.2, 7.7, 8.6, 11.3 and 16.4 μm, and atomic fine-structure lines of [ArII] 7.0 μm, [ArIII] 9.0 μm, [SIV] 10.5 μm, [NeII] 12.8 μm and [NeIII] 15.6 μm. The spectra were decomposed by fitting a combination of Lorentzian line profiles and a blackbody curve to the data to produce maps of the spatial distribution of the fine-structure and UIB emission features. These maps have been compared with VLA radio, 450 μm SCUBA maps, 12CO () maps, and broadband filters ISOCAM LW2 (5–8.5 μm) and LW3 (12–18 μm) observations. Decomposed spectral features have shown that the LW2 filter is dominated by UIB emission and the emission observed in the LW3 filter is a combination of Neon fine-structure lines and a steep continuum, with the continuum dominating. Using the photoionisation code CLOUDY we have produced theoretical values for the fine-structure ratio of [NeIII] 15.6 μm/[NeII] 12.8 μm, from which we have calculated the effective ionising flux impinging onto the tips of the pillars to be ~ photons cm-2 s-1, consistent with estimates made from VLA observations.
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