ISOCAM-CVF imaging of M 16

Free access article

Issue		A&A 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. White^{1, 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)

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 $^{\prime\prime}$ . 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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