AAS 195th Meeting, January 2000
Session 74. ISM: Dust
Display, Friday, January 14, 2000, 9:20am-6:30pm, Grand Hall

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[74.07] Dust continuum and features in ISO-SWS 2.5--45\mum spectra of galaxies -- templates for SIRTF and other missions.

E. Sturm, D. Lutz, D. Tran, H. Feuchtgruber, R. Genzel, D. Kunze (MPE), A.F.M. Moorwood (ESO), M.D. Thornley (NRAO)

We present an inventory of mid-infrared spectral features detected in high resolution (R~1500) ISO-SWS 2.4--45\mum spectra of the galaxies {M\,82}, {NGC\,253}, {Circinus}, {NGC\,1068}, and the {30\,Doradus} region of the LMC. We discuss their identifications and highlight possible relations between these features and the physical state of the interstellar medium in galaxies. In the 5--13\mum region, emission from unidentified infrared bands (UIBs), usually ascribed to aromatic molecules, and apparent silicate absorption dominate the spectrum. The density of features makes it difficult to determine the continuum, particularly in ground-based data of limited wavelength coverage. In fact the apparent depth of the 9.7\mum silicate absorption may be overestimated in the presence of UIB emission, as we demonstrate by comparing the spectrum of M\,82 to the (absorption free) spectrum of the reflection nebula {NGC\,7023}. No strong silicate absorption is present in M\,82. The (very small grain) dust continuum under the UIB emission in our starburst templates can be modeled by a simple power law, starting at wavelengths between 8 and 9\mum. Differences in absorption features point to different physical conditions in the obscuring regions of active galaxies compared to starburst galaxies.

The spectra are valuable templates for other mid-infrared missions. We smooth our data to simulate low resolution spectra as obtained with ISOCAM-CVF, ISOPHOT-S, and in the future with the low resolution mode of SIRTF-IRS, and use our high spectral resolution information to highlight possible identification problems at low resolving power that are caused by coincidences of lines and features.

The author(s) of this abstract have provided an email address for comments about the abstract: sturm@mpe.mpg.de

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