EDP Sciences
Free access
Volume 409, Number 1, October I 2003
Page(s) 193 - 203
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20031076

A&A 409, 193-203 (2003)
DOI: 10.1051/0004-6361:20031076

ISOCAM-CVF imaging of M 16

J. S. Urquhart1, Glenn J. White1, 2, G. L. Pilbratt3 and C. V. M. Fridlund3

1  Centre for Astrophysics and Planetary Science, School of Physical Sciences, University of Kent, Canterbury, CT2 7NR, UK
2  Stockholm Observatory, Department of Astronomy, 106 91 Stockholm, Sweden
3  ESA Astrophysics Missions Division, Research and Science Support Department, ESTEC, PO Box 299, 2200 AG Noordwijk, The Netherlands

(Received 15 April 2003 / Accepted 2 July 2003)

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 $^{\prime\prime}$. 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 ( $\emph{J} = 1{-}0$) 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 [NeIII] 15.6  $\mu$m/[NeII] 12.8  $\mu$m, from which we have calculated the effective ionising flux impinging onto the tips of the pillars to be ~ $1{-}3\times10 ^{10}$ photons cm -2 s -1, consistent with estimates made from VLA observations.

Key words: ISM: HII regions -- ISM: lines and bands -- infrared: ISM -- ISM: individual object: Eagle Nebula

Offprint request: J. S. Urquhart, jsu@star.ukc.ac.uk

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