ISOCAM-CVF imaging of M16

We present ISOCAM observations (5 - 17 mum) of the HST M16 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 similar to 40 (lambda/Deltalambda) 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 mum, and atomic fine-structure lines of [ArII] 7.0 mum, [ArIII] 9.0 mum, [SIV] 10.5 mum, [NeII] 12.8 mum and [NeIII] 15.6 mum. 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 mum SCUBA maps, (CO)-C-12 (J = 1-0) maps, and broadband filters ISOCAM LW2 (5 - 8.5 mum) and LW3 (12 - 18 mum) 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 mum /[NeII] 12.8 mum, from which we have calculated the effective ionising flux impinging onto the tips of the pillars to be similar to 1-3 x 10(10) photons cm(-2) s(-1), consistent with estimates made from VLA observations.