ISOCAM-CVF imaging of M 16

Urquhart, J. S.; White, Glenn J.; Pilbratt, G. L. and Fridlund, C. V. M. (2003). ISOCAM-CVF imaging of M 16. Astronomy & Astrophysics, 409(1) pp. 193–203.



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 (λ/Δλ) 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 μ m, 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 ( J = 1-0) 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 μ m, from which we have calculated the effective ionising flux impinging onto the tips of the pillars to be ~ 1-3 x 10 10 photons cm -2 s -1, consistent with estimates made from VLA observations.

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