Institut d'Astrophysique Spatiale, UMR-8617, Université Paris-Sud, bâtiment 121, 91405 Orsay Cedex, France e-mail: email@example.com
2 Gemini Observatory, 670 North Aòhoku Place, Hilo, HI 96720, USA
3 Laboratoire de Photophysique Moléculaire, UPR 3361, Université Paris-Sud, bâtiment 210, 91405 Orsay Cedex, France
4 Service d'Aéronomie, UMR 7620, Route des Gatines, BP 3, 91371 Verrières Le Buisson, France
Accepted: 22 November 2006
We analyze dust features present in the mid-infrared (Spitzer) and recently published L-band (UKIRT) spectra of the infrared galaxy IRAS 08572+3915. The line of sight toward the AGN nucleus crosses a high column density of carbonaceous dust whose characteristic absorption features appear clearly. They provide a real insight into the chemical environment of the diffuse interstellar medium. Thanks to the moderate redshift of IRAS 08572+3915, the wavelength of the aromatic CH stretching mode is free of major telluric lines, and a strong observational constraint of H/H has been determined. This limit clearly shows that the bonding of hydrogen atoms in interstellar hydrogenated amorphous carbon is highly aliphatic. The presence of a broad absorption feature centered at 6.2 μm, probably arising from olefinic/aromatic structures, corresponds to the backbone of this carbonaceous material, which is the major carbon-containing component of the interstellar medium along this line of sight.
Key words: ISM: abundances / ISM: dust, extinction / galaxies: individual: IRAS 08572+3915 / galaxies: ISM
Based on observations made with the Spitzer Space Telescope (GO-3336 program), which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407.
Based on data obtained at the United Kingdom Infrared Telescope, which is operated by the Joint Astronomy Center on behalf of the UK Particle Physics and Astronomy Research Council.
Part of this work has been financed by the french CNRS program "Physique et Chimie du Milieu Interstellaire" (PCMI-CNRS). TRG's esearch is supported by the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., on behalf of the international Gemini partnership of Argentina, Australia, Brazil, Canada, Chile, the United Kingdom, and the United States of America.
© ESO, 2007