ISOCAM-CVF imaging of M 16

Abstract

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

Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands and the UK) and with the participation of ISAS and NASA.